is my computer good for gaming ?

Yes. Do you already own these parts? I would make a few small changes.

Yeah that is plenty good for gaming. I would tweak it a bit if I were you, but it's up to you.
Here is something to consider (not sure on your budget or what country your ordering from but...):

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-4570 3.2GHz Quad-Core Processor ($179.99 @ Amazon)
Motherboard: ASRock Z87 Pro3 ATX LGA1150 Motherboard ($84.99 @ Newegg)
Memory: G.Skill Ares Series 8GB (2 x 4GB) DDR3-1600 Memory ($68.99 @ Newegg)
Storage: Crucial M500 120GB 2.5" Solid State Disk ($73.99 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($54.99 @ Amazon)
Video Card: EVGA GeForce GTX 780 3GB ACX Video Card ($499.99 @ Newegg)
Case: Corsair 200R ATX Mid Tower Case ($59.99 @ Newegg)
Power Supply: Corsair Builder 600W 80+ Bronze Certified ATX Power Supply ($37.99 @ Newegg)
Total: $1060.92
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-04-27 17:31 EDT-0400)

Performance - 8/10
Value - 5/10

This is how I would rate the parts:
Components:
8-9 = I would have probably got the cheaper 4 core i5 4570 for about $180 (should perform close enough to the 4670k, just no OC'ing)
CPU: i5 4670k

8-9 = I would have decided on a different Mobo, but this one isn't too bad. I prefer to spend a bit less here and use the extra $ for other parts.
Motherboard: Asus Z87-A

9-10 = Depending on the model, I would have made sure to have low profile heat spreaders and also make sure they run at 1.5v (stock voltage) and at CAS 9 @ 1600 mHz.
Ram: Gskill Ripjaws X 2×4gb

9-10 = I'm not sure the 4 gb's is needed, but I'm sure there will situations where it "might" come in handy. I would have considered the R9 280x or R9 290 personally, but this GPU is a good option too.
GPU: gigabyte GTX 770 OC 4gb

8-9 = This HD is a pretty quick one, but you usually spend a bit more on it. I would have considered the WD Blue drive for less and used the extra $ for a bigger SSD (120 gb at least).
Hard drive: WD Black 1TB

7-8 = I'm not a proponent of small SSD's these days. The Crucial M500 120 gb SSD has been around $80 these days and makes the most sense to me for the cost and size. Windows 7/8 install size is around 15-20 gb's and by the time you do updates and a few necessary apps your looking at around 30-50 gb's in size (depending on what you have). I would much rather have the SSD at 50-60% capacity rather than 85-95% capacity.
SSD: Kingston 60gb

8-9 = Antec makes decent to good PSU's and supports them pretty good (from my experiences). 900w PSU is just too much, IMHO, for this build. It would support SLI in the future, but I believe your better off with single GPU solutions all around. You spend less $ on cooling the parts and less on the PSU needed too, but that is my opinion.
PSU: Antec high current gaming 900w

8-9 = This case is quite the beast, but I tend to save some $ here and use it for other upgrades. I generally look at Corsair 200R/300R as starting points. Those 2 cases are usually around $40-60 and are built pretty good for the $.
Case: Cooler Master CM storm 690 III

8-9 = This is one of the better coolers, but honestly I don't think it is necessary, unless your going to OC the 4670k. I tend to run at stock settings (because stock CPU's these days are pretty good) so I can run at decent temps and also so I don't have to spend more $ to keep them cooler. Now if you want the upgraded cooler for a bit quieter operation, I can understand that. I would opt for the CM 212 EVO (around $30) for 95% of uses and situations, but that is just me.
CPU cooler: Noctua NH-D14

Overall I would give you a 8-9 rating on your options that bought. Like I have listed above and also mention by another poster, I would have done things a bit different, but that is the beauty of having options and opinions. Everyone has them and none of them are necessarily bad.

Hopefully I have helped out in some way?

Yeah SLI/Crossfire is nice to have, but I don't think it's worth it, IMHO, but to each his own. Your overall build is pretty good, so you should feel pretty good about the parts that you got.