It's not good for games that benefit from one or two strong cores. It's not that bad, though, but I honestly wouldn't buy one. I will say it can be decent competition in applications that take advantage of all of its cores.
Best case scenario it's a hair faster than an i3. Worst case scenario it's 30-60% slower. It's true that it's unlocked but for what it would cost you to get any solid clocks out of it (more than just a barebones board since AMD boards house the VRMs where intel has them right on the CPU, you'll also need a cooler) you'd be better off just buying a locked i5 and a compatible cheap intel chipset board.
At the end of the day most games are GPU bound and that's not going to change whether you get an i3 or 6300 or 8 core extreme edition i7. CPU intensive games like SC2, modded minecraft, Civ V, etc etc, are going to crawl when it comes to the wire (civ v is a bit of a special case, the frame rates won't actually dip. NPC turns will just start taking 10-15 minutes vs 5-10 on the comparable intel part).
Most games aren't that heavily threaded, including the ones I listed above who benefit from 3, 1, 2 strong threads respectively, there is the occasional BF4 that does benefit greatly from extra threads but apparently it has issues with 6 thread processors, or did at least, so that doesn't score many points for the 6300. Personally, I'll take the i3 every time for a gaming rig since it's better in most situations (even if it's not noticeably better), not that far behind when it isn't ahead, uses half as much power, and has integrated graphics to fall back on if something happens to your gpu.
Every time I try to go where I really wanna be it's already where I am, 'cuz I'm already there XBL, PSN, Steam, Origin, BSN, GFAQs, MC: PhilOnDez
I've played complete civ5 games and found no instance of npc turns taking even 2 minutes. But hey, I'm probably wrong since I've only been using an un clocked 6300 for a year and these other guys never had one in there PC(s).
Is a locked i5 better. Ummm...durrrr of course it is. Is it the best CPU out there. Of course not. At a certain budget it is a solid choice. But I read some crazy things about it that I've never once experienced. I have 144 games on steam. My 6300/7850 budget loser build plays all at least on high. My twitch sn is same as steam if you want to see what games a 6300 can play.