Stage 1 is some pretty fixated platforming which has an overall nice balance of difficulty. None of the saves are that much harder to do than any other. It's also reasonably fun and looks very clean. Stage 2 is kind of an upgrade to the difficulty, but it's about as possible for someone who has the skill level to beat the first one. Not to mention that the graphics and music are also very comforting. Stage 3 boosts the difficulty quite a bit, now involving saves made of legitimate hard jumps. There's also a water save which can get you stuck for a while. The graphics are less interesting, and the needle design definitely becomes more compact.
Finally, the fourth stage is easily the hardest. It's got saves with minimal gimmicks, but the jumps involved are precise enough to make the saves just that much harder. There's lots of places to choke, but if you can pull it off, it's very fun. The last save is my only quarrel, but who knows, it might have been in an earlier version. The last save isn't all that well designed. Other than that, Ariotrap 2 is a fun game to play. I would recommend it to players who think they are capable of taking on hard needle games.
EDIT: holy god, his game gets really spicy near the end, that's pretty hard.
Stage One is the best part of the game, with an interesting level design and jumps that look really intimidating without being that hard. Stage Two has more traditional jumps, but they're placed in original ways. Stage Three is a large increase in difficulty, and has some unforgiving water segments. Stage Four is where I have a few issues with design. Most saves are really well made (the second save was my favorite one in the whole game), but the second save of the second screen has one of the worst platform placements I have ever seen. The last save is tedious and boring, and the spikes in this stage have a huge glow around them that makes some of the tighter jumps hard to see.
It's a lot harder than the first, and despite a few flaws in Stage Four, I'd recommend it to anyone who likes challenging needle.
Edit: New version polished out these issues. :)