Nice to haves:
Allow editing notes in replayer
Add street buttons in replayer (click in street to move to start of street)
Give some reward for krill 50, as far as I can tell you get nothing for it now (no rake improvement and no freerolls)
Make the color labeling a bit more distinct in the UI
Yeah, the hand replayer is dire and IMO it cannot be fixed in the current form, it has to be rewritten from scratch.
Some points
- Jump buttons to streets and showdown according to game type (Preflop/Flop/Turn/River/Showdown in HE and Omaha, betting and drawing rounds in draw games, streets in stud games ...)
- Display all known cards, final pot size and outcome (win/loss tally for each player) at any point during the replay. You can add a "hide spoilers" option but IMO it's more useful to know these things in order to decide whether the hand is worth reviewing or not).
- Navigate back and forth and jump to preset points quickly, without having to endure any animations or delays. The "movie mode" replay where you click a play button and wait for stuff to happen is the worst. It may be useful to some but it should never be the default.
- Database browser where you can sort, search and filter hands according to game type, pot size, outcome, hole cards, players involved, whether the hand went to showdown and if not the street where it ended etc.
I concur with the color coding suggestion, one more thing: the color choice is uninspired, for example Violet and Fuchsia look about the same.