1) When watching story movies I noticed that some sprites were scaled using Nearest Neighbor algorithm, that resulted in very blocky image (e.g. Lee on first two screenshots).
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2) Highscores caching (at least global ones). It usually takes 2-5 seconds to load just one screen (but sometimes up to one 1 minute).
Total score is updating every time it appears (e.g. go to rewards and go back), it annoys a lot. Old data is better than no data at all...

3) Songs preview. In all music games I've played before when you select the song you instantly can hear it. It helps a lot when choosing a track... I hope it can be added. It would be especially helpful for "Beat Your Music" mode (when selecting song to import and when choosing between already imported songs).

4) Sorting options in "Beat Your Music" mode. I've imported 20 songs (out of ~100 that I prepared) and I'm getting lost already. Or just sort them alphabetically by default.

5) Also some options to rate imported song would be great. Some generated tracks were fine, some were good, some were bad. But I can't remember which ones...

6) Support for any number as Beat Start, or, at least, 10 seconds limit.

7) And just random question. Is it possible to read ID3v2 tags? I've read that it's possible to store a lof of data there (more than 1-2 KB). I'm wondering if it could be possible to use them for storing beatmap (enemies types and timing)...