One thing I usually hate is levelling up and buying equipment in action games. The worst cases are almost always beat em ups, a genre that has been completely killed in recent years by developers choosing to replace interesting mechanics and design with endless grinding and enemies that can only be defeated using moves that are only useful for defeating those specific enemies. But I'm going on a bit of an unrelated rant here, as though Olteus II has both experience levels and a weapon shop, they actually make the game more compelling. Plus it's a shooting game, not a beat em up.
In fact, the way the game seems to encourage, rather than punish continuing in contradiction to the genre's norm, it can possibly be considered a kind of dialogue-free action RPG that takes a shooting game-like form. For shooting enemies, you gain experience points and gold. Levelling up via experience increases the amount of hits you can take before dying, and increases the power of your default gun and your charge weapon. You also start the game with two options which do nothing alone. This is where the gold comes into play: there's a shop with a variety of different weapons, and different power levels for each of those weapons, and you can equip a different weapon to each one of the options.
The game's split (as far as I can tell, as I haven't completed it yet) into two planets, of four stages each, and a final techno-organic spaceship with a single stage. The stages on each planet can be done in any order, though you have to complete one planet to go to the next. There's also a system of "days" in effect. You start with 999 days to complete your mission, and every time you play a stage, whether successful or not, takes up one day. I really don't know what happens if you run out of days, as getting to the final stage, maxing out my level and getting enough gold to buy every weapon took about 20-something days and an hour and a half. It'd take superhuman levels of both incompetence and persistence to get through 999 days.
The game's presentation is definitely a strong point. The menus all look great, with little diagrams for the weapons in the shop, and thumbnail illustrations of each stage on the stage select screen. Ingame, it looks really great and very colourful, and though it's a minor shame there isn't any parallax, it does look amazing for an independently-produced videogame from 1991. The music was a surprise, as it sounds like it was influenced more by western computer game music, rather than the arcade and console influences you see in most X68000 games (and especially shooting games).
In summary, Olteus II's idiosyncracies mean it won't be something you'll play for years to come like the more orthodox high-quality shooting games on the X68000, like Cho Ren Sha 68k and the like, but it is an entertaining way to pass a couple of hours.