To Robert about your dynamite idea:
That was already invented in another old DOS Game with similar graphics and block-levels as this, but you use dynamite to get to the exit. It was way fun. If you want to know what I’m talking about you can get it here:
http://www.dosgamesarchive.com/download/the-tunnelman/

But I digress, yes the phaser needs to stay.

Having been away for a while, I have only now got time to chip in, but I wanted to make sure I do.

Here are some of the thoughts that came to mind in connection with your post. What I write below is based on three things. One, the experience from the past fifteen-twenty years related to playing (and sometimes, testing) hundreds of professional and amateur action/platformer games. Two, the couple years I spent creating amateur games in the genre, and three, the time I spent with the theory and analysis of computer and video game genres.

First of all, you are spot on with the nonviolent vibe. The fact that there is no way for the player to directly kill or otherwise dispose of the monsters, coupled with the one-touch-death rule pushes the game into the positive side of retro — it is an old-school ruleset which makes the game challenging, but, with a good learning curve, good level design and fair physics (e.g. good pixel detection), it still does not make it irritating by default.
As a side-note, many game creators that have chosen to go ‘retro’ have taken up the idea that implementing old systemic limitations (like not being able to save, bad collision detection or fake loading times) would generate the same nostalgic effect in gamers — it usually only brings back the same irritation one had back then. (Retro Game Challenge or the recent Bit Boy are perfect examples for this.) So there is a fine balance between true nostalgic old-school gaming and old, irritating designer habits. Carefully implementing these parts of the old Jetpack will prove to be fruitful and will attest to a true old-school brand (players saying “this is just as cool as the old one” is always a good marketing point).

Secondly, the phase shifter. While based on the Lode Runner ability, it is much more sophisticated than that. First of all, you can phase in four directions, you can phase while using the jetpack (creating wonderful player tension when you have to phase while flying and glimpsing every moment to see whether your fuel has run out), and there is the degree of variation in phasing times for the different blocks. Doing puzzles with the pink blocks, the different return times for bricks, the wooden boxes; also trapping enemies or creating different paths for them, and even timing the level so that you can phase a block at the exact time for an enemy to behave in a specific way, these are all elements that are at the foundation of the original Jetpack game. Personally, I think this is hands down the most unique element in Jetpack, something I have not seen in any game ever since.

Keys. As you said, 95% of games have guns. It’s a too easy choice for the developer to put a gun in there, and will not make the game unique. However, in the action, platformer and puzzle games the same is exactly true for keys. They’re absolutely overused, they’re an easy way out for the developer, and have been for as long as I know.
Interestingly, that bring us to another unique selling point of the original Jetpack. Like the phase shifter was a very clever and multi-layered upgrade to the Lode Runner ability, switches are a simply brilliant upgrade to the key problem. You can seal off one or more parts of the level, and have either the player, or — even better — let either the player OR the monsters be able to turn it back on. I don’t remember any other game having it like this, and I know that back then I’ve found this insanely innovative.
If you ask for my personal opinion, I would say that you should avoid keys entirely and keep the switch system, which is highly modifiable and would be fun to play around with some more, like switches working for specific areas only, switches that stay jammed, switches that turn off normal blocks or even turn off enemies, etc. The possibilities are limitless, while with the one-time use switch you still have the same functionality as the key.

Other items. While I dislike guns and any ability to kill enemies, there is a possibility that enemy hindering abilities would work. There is proof for this, the temporary invincibility and enemy-freezing items worked pretty well in the original game and I would keep them, although not as randomly appearing items at all (I don’t know if I have mentioned this already, but the only aspect of the game I would surely want to remove is the random appearing items as they often disrupt the level design). Using them as strategically placeable items would create another strategy for the player to get through puzzles and for the developer to create puzzles. Like phasing, there is a specific time before the player’s invincibility runs out (and if there is no visible counter for it like in the old days, it’s all the better), so the player will have to keep track of the time. Again, challenging aspect, positive game-related tension. All good gaming.

A good rule with action-platformer games is to “keep it simple”. Too many types of items, power-ups, or modifiers can and will ruin the game, especially if they serve the same function (ie. if you have a switch system, you may not want to have a key system as well, because they mostly serve the same function; only use both if you can strongly support the idea that you really need both). I’ve often seen that when many types of stuff are available, level design gets sloppier over time and starts to rely too much on the items, power-ups or modifiers. Also, there is a reflex in the player when seeing item#15, “oh, here’s an item#15 level again”. This, again, can be overturned with brilliant level design, but there is always this danger lurking in the corner.
The same rule does not apply if items, power-ups and modifiers are carefully balanced out, and they also do not become redundant. For an example outside of the genre, see Popcap’s recent and brilliant Plants vs. Zombies. There is a very clever build-up of items as well as enemies, but it does not become overwhelming because a., the basic system stays simple and b., every item and enemy stays truly unique.
Also, this game offers a very good system of “problem first-solution later” level design, echoed in Ron Gilbert’s rules for graphic adventure games, written decades ago. It also applies to platformers in that you get a better play experience if you see the problem first and have to start to think of a solution before you actually come across a solution. In such a game as Jetpack you would first face an obstacle or sealed-off area before gaining insight into how to actually get there.

All in all, I think the original Jetpack had a very well put together system of items and powerups that could use little tweaks but overall there should not be big chunks taken out of it. The jetpack and it’s fuel refills work great (while no-jetpack and just jumping levels were one of my great favourites), the phasing system is brilliant, and the switch system, while it could use some flexibility upgrades, could also go a long way. Not mentioned before, the teleport system is also something that is entirely unique (especially with many teleports randomizing input and output points), and should also be kept. Enemies should not be destroyable but should be hinderable for a short time (the original powerups are good here as well, if a freeze ray should be implemented it should be only give the player short range and a few chances or a short amount of time to use it before the button returned to the normal phaser).
The new physics engine could enable new things like crumbling blocks. Bombs also sound fun, and playing around with lighting would also be an interesting idea (moving light sources, etc). Still, I would definitely keep intact all the things that were not only working but brilliantly working in the old game.

That’s all for now, I hope you find some of the above ideas useful. As always, I’m quite up for discussion of any of the above points.

You are the plus sign, the dynamite is the quatation mark, and all of the lines make up rows and columns of bricks.
______________
| |________________[where you want to go]______
________________ +_”| ________________
___________________________________________________

When the dynamite is set off, the column it’s next to collapses, bringing it down onto the row below the one you’re standing on, and allowing you to jump up and walk across.

That probably seems a little too complicated for jetpack, but it’s just something I wanted to bring up, and you can use it however you like.

Fire sounds alright, and I like the idea of having extinguishable fire. Maybe you could add some fire jets in some of the levels that you have to time to get past.

The flashlight idea reminded me of the dark room in GoT, where all you could see were Thor’s eyes (and I thought it was hilarious when he hit the shovel and his eye looked smashed and throbbed); I’m sure you already planned on it being this way but I think the flashlight should have a limited cone or ray of light, and MAYBE it can have a meter (battery meter) so you can only use it for a certain amount of time – like the jetpack in the original jetpack. Of course you could add more batteries as pickups to give you back your light – or maybe even a stationary place where you can charge up your flashlight instead (or in addition to…)!

I think any baddies with lasers (like trak-bot or w/e and homer) should have their lasers visible in the dark; it would be a nice, logical twist.

Also…a timed shield that you could move around with could have its uses – but what would happen if a monster ran into you? would it change direction like the missile, or keep trying to get at you like trac-bot or just hover around like the boxer?! I guess you wouldn’t be standing in one place for long, but I guess that could be in levels or in places without monsters that follow you.

Can’t wait to see what you do, Adam!

Yeah the random monster avatars are a little cheesy but I dig em.