Johnyqd, LOVED your post! Thanks for sharing your thoughts!
Can you give a comparison for Graceful Explosion Machine? It looks like/reminds me of Pixel Junk Shooter... it's bright and colorful and you're shooting in all directions. Are there bosses in the game, or is it straight hordes of bad guys in all directions and you're fending them off.
Thumper really has me interested, I love music rhythm games (Theathrym FF was my favorite on 3DS), but the $20 price tag is scaring me off. Is there much to "do" in that game other than replay stages and go for bigger scores, and are there leaderboards or unlocks of any kind?
I do see the similarity between the art (and controls) in GEM and Pixel Junk Shooter. It actually plays a bit more like Resogun (circular stages, aiming for clean/full combo runs). There aren't bosses, but as the game progresses there is a change in focus from swarms of low hp enemies to some truly nasty higher hp foes.
The beauty in GEM is that it is a constant challenge to use the right weapon at the right time. You have a basic blaster that does low damage and charges quickly when you aren't using it. The other three weapons all share an ammo pool which is filled by collecting dots picked up after destroying enemies (a laser for high hp enemies, a rotating sword for big groups, and homing missiles). The first couple levels you can just pew-pew and keep a combo going, very soon you realize you have to keep switching between basic and special weapons, and in the final third of the game you have to be very specific in which weapon you use at what time (all while frantically trying to survive waves of enemies).
The game is expertly balanced and really shines when you work to get full combos on the levels (combos only last if you keep killing enemies quickly and don't get hit by enemies).
I'm an Elite Beat Agents kinda guy, HarmoKnight on 3DS was pretty great too. Unlike many other rhythm games Thumper has a very distinct style and sound which is consistent through the levels. I don't knock it for that style, but it is a very different beast then more stylized song/themed games.
In terms of value - Thumper is made up of 9 "worlds", each with about 20 - 30 "levels". Now for a comparison that could get me into hot water: each level is kind of like a Super Mario Brothers level in length (an auto scroller obviously), some of the levels in each world are bosses. So, if you would find value in a fiendishly hard and very intense rhythm game that is multiple times the length of the original SMB, then don't hesitate to buy Thumper (even if you never replay a single level for a better score).
There are also leaderboards and unlockable challenge modes for each world. Also, the game by default restarts the level you are on if you fail or restart. I finished up the first world getting "S" rank on each level and was astonished to see my low placement on the leaderboards - the reason is that you get multipliers for beating consecutive levels without restarting/dying - so to get a truly high score in a world you need to die as little as possible.