Via [url=http://blog.counter-strike.net/index.php/2015/04/11936/]the CS:GO blog[/url]:

[quote=Valve][b][i]GAMEPLAY[/i][/b]
- Fixed a few cases where reserve ammo was shared between multiple weapons. All weapons now individually handle their own reserve ammo.
- sv_autobuyammo now defaults to 0.
- If a player spawns with a smoke grenade in classic competitive, it counts toward their maximum smoke grenade purchases for that round (i.e., they cannot purchase a second smoke grenade).
- Fixed HE grenade particle system drawing improperly sometimes with other particle systems (like smokes volumes).

[b][i]MISC[/i][/b]
- Added 10 new community sticker offers, and a new community sticker capsule featuring work by Enfu.
- Added support for alternative voice communication codecs. While running a server, use +sv_voicecodec vaudio_celt to use the CELT voice codec, instead of the Speex codec which is used by default.
- Added support for Phong on world materials. See Train for examples of such materials.[/quote]

Rumor has it:

- Images of the new stickers can be found on CS:GO Stash [url=http://csgostash.com/stickers/capsule/49/Enfu-Sticker-Capsule]here[/url] and [url=http://csgostash.com/stickers/community/Community+Stickers+Series+5]over here[/url]

- New flavor text got added, TyroPyro dumped them for your convenience: http://www.reddit.com/r/GlobalOffensive/comments/347uvq/counterstrike_global_offensive_update_for_42815/cqs8a4n

- Item schema update: https://github.com/SteamDatabase/SteamTracking/commit/d0c3314a0533e44d1094cb7b28c8b13db7474fbb

- Strings and other stuff: https://github.com/SteamDatabase/GameTracking/commit/a3838e1c1f850fca45086241457bbe4de12fd141

- Size is ~300 MB - [b]data capped users should be aware[/b]