By priority IMO:
1. Integration of external server browser to make in-game one have similar functionality:
Quickly implemented sorting helps quite a bit, but it still isn't what most other games provide. Lack of other ways of sorting (mostly to find servers by name) and searching on the fly is one thing, but password protection/GLS setting are pretty crucial informations to have.
2. Visual improvements:
Besides HR4 pack, there should be more:
-anti aliasing (on certain maps jaggies are not only visible but really annoying),
-bloom (gives great effects if not overused)
-better quality weapon models
-various minor effects (colored smoke grenades, CO2 escaping from muzzle, etc)
3. Tutorial - good idea, if you reuse shaztrain map, that should not take too long.
4. Bot AI - personally, I don't think many people play with bots as it is, but I play other game (Xonotic) that catches currently a lot of hell for bot AI, and it has much better AI than this one. There should be navigational data (waypoints) provided in the map, and bots should at least follow those. It will get trickier for flag modes, because bots should not follow those nodes randomly, but approach flags consistently. I don't think accuracy is much of an issue, but it would be good if bots could bunnyhop efficiently.
As providing waypoints is mappers' responsibility, and some may have left this game long ago, it would be ideal to be able to add waypoints in-game.
5. Jump mod - definitely very good idea, but probably would be best to work over previous ones first.
Playback/jerseys are certainly good thing to have, but are rather minor stuff compared to listed aspects. Actually, jerseys fall very much in visual improvements.
EDIT: I do not have Win 7, but if people can't get to run game at all, that would be biggest of them all.