This is a great pool player's pool hall. It's a bit odd that you don't see more 'serious' players; the dominant clientele seems to be kids on dates, but that's true of all the pool halls around downtown.
The rates are the best I've found ($3.50/hr weekends, $7/hr weekdays). They have 8 full size Brunswick tables for pool and 8 snooker tables, and it's really only busy on weekends after 9 or so. I've only had to wait for a table once. The pool tables are in decent shape, some dodgy rolls and dead rails but nothing disastrous.
Since it's an actual pool hall there's no point in coming here if you're not playing, but their food and drink is surprisingly good for it and well-priced. Sandwich and fries will set you back about $6, $3.50-$4 for a bottle of beer.
Ambience here beats VIP Billiards hands down; prices beat the otherwise-lovely Charlotte Room. The hall at the Rivoli is a good comparison, the tables are in similar shape, but Annex wins because Rivoli has a full bar and loud music that causes commotion in the pool hall in the evenings. At Annex the music is 97.3 (the 80s station) at a tastefully low volume, which is A-OK with me.
Slightly better maintenance on the tables and more actual pool players would make this a top tier pool hall. As it is, it's good enough to be my go-to accessible-by-subway place.