Sonic Wings 3, killer soundtrack but hellish difficulty. I also played a lot of Viewpoint and i can make it to lvl 3 but that's about it, also killer soundtrack.
If you're playing SW3 on European difficulty, it's tuned differently than US or JPN. On US or JPN region, even on difficulty level 8, SW3 is very much in line with the second game in terms of overall difficulty. This might be the issue you're running into. If you're playing on a console/MVS with a Unibios, it defaults to European I believe, so you'd need to change the region to US or JPN manually. Quite a fun game once you overcome this little quirk. Not sure if this is a weird region glitch or what, but the EU code makes the game nigh impossible. I made a video about this a few years back.
For me, Pulstar. The graphics and sound are excellent - That doesn't save the game from being a boring slog of a run with one of the worst checkpoint systems I've countered in a shmup along with poor powerup placement. Beatable, yes, but who on earth has that amount of time or patience? It's not impossible, sure, I've tried countless times and I just can't jive with it.