Woah, I totally didn't expect responses showing up this time. I guess persistence pays off!
First thanks all commenting on the art. It seems to be one of the stronger points of the game and I've gotten a lot of positive feedback about it, including sooo many comparisons to Plants Vs Zombies. PvsZ was an awesome game (once people started making the comparison, I bought it on Steam and plowed through that game and its extra modes) and I know mine bears a few particular similarities, particularly in the row-based defense and enemy progressions. I probably learned a few design ideas from it too!
supershigi: The jetpack minigame is odd and needs to be "felt". It's pretty much your first fret/drum speeds your jetpack up (to get further distances faster), while the other 3 frets transition you between top, bottom, and middle of the screen height. Beyond that it's just an avoidance game. I may need to add color indicators to help show which buttons move the character to which locations. Did I mention PvsZ is awesome and I've listened to that music video like 50 times?
Hideous: I regret to admit I'm guilty of that too. Now I feel bad
HybridMind: It's single player. The timing line pretty much maps to if dots converge, that's a beat (as Ryx mentions, it's mostly a 4/4 tempo). There are colored pads below each column of units, where hitting that colored pad on the beat will activate that column's weapons (if recharged).
Ryx: Glad to hear you played it. Most of the game stays on that 4/4 beat (with certain sections having pauses). This is definitely a concern I have. The game is paced such that it does start off fairly easy, if you can just maintain that rhythm. Later on comes more challenge in which units you use but it really needs to be more compelling from the get go. The big issues I see are for one, I need to introduce new weapons at a pace that the player can understand the gameplay and weapon strengths, and secondly I can't map the beats like GH or RB would because it causes too much of a disconnect in players' visual focus. In that respect I go with the 4/4 beats, kinda like Patapon. This is something I've been wrestling with for a while (nearly since the start), so I'm honestly unsure if I'll be able to come up with an adequate solution to this problem :/.
Thanks for the opinions everyone! I keep feeling like I need to wrap this project up (6 months full time is too long for my projects!) but I really want things to "feel" right for players when it finally comes out.