I started this game for the first time 3 years ago and finally completed it. It is the most challenging of your games from this series. I mostly liked the variety of challenges.
But as many people already mentioned its main problems are the controls and mechanics. This is why I had to approach this game... you even wouldn't be able to imagine how many times... The biggest problems:
1. If you are standing next to the wall with the finger pointed towards it and try to jump you will most likely hit/get stucked on some invisible obstacle or stick to the wall for no reason. The same is for the mid-air rotations you are performing close to the wall. When you got unlimited time it is not a big deal, but on those levels with a time limit... I especially hated level 9 because of that issue and almost raged again for another 3 years. Also the mid-air control could be improved.
2. It sometimes happens that you get stucked on some invisible hardness on the ground while trying to move left/right and there is no other way than jump out of that place.
3. You may also stick to the ledges when trying to jump out of them.
There is also one important problem with bonus 3 that left me confused for a longer moment.
What's the problem? You may actually accidentally destroy a spaceship BEFORE it will even enter the screen or on its border and when you do the game DOES NOT count it as destroyed. So you have to make the game a bit harder for yourself by letting all the ships fully enter the screen and count the shots needed to destroy a pack of spaceships. The good thing is that you need only one shot to destroy a triangular one. For everybody that would have problems with this stage: during wave 1 you need to destroy 19 enemies and after wave 2 you need to have a total of 47 enemies destroyed. If you are absolutely sure that none of them escaped the screen and you got less kills than required - then you probably killed some of them out of the screen and the stage will reset.