I will give my opinion. Yes, it's a very old machine. Very out-dated technology. That CPU was fantastic when it came out but by today's standards both the CPU and the front side bus it runs on are turtles. Also your monitor resolution is very mid-to-late 90s, like EarthDog said.
It doesn't sound like you play very demanding games so as long as you stick to that, you should be fine. The question is whether you feel like you want more, and whether you want to spend the money on upgrading.
There are 165Hz (and more Hz even than that) screens now with adaptive sync. Monitors have really become spectacular of late. There are video cards with several orders of magnitude more power than the one you have, and there are CPUs that are much more powerful. RAM is faster. Data moves around the motherboard faster. There are better storage interfaces for blazing fast solid state storage... the list goes on and on.
I think that if you had something like a 6600K on a Z170 board with 16GB of DDR4, a GTX 1070 GPU, a nice big fast SSD, and a high resolution, large, G-sync monitor, as well as some nice gaming gear in the form of a Corsair K70 keyboard and a nice gaming mouse, you'd probably have a lot more fun, and your mind would be utterly blown and remain so for quite some time.
The question isn't whether it's worth it to us, because it is. Most of us here love high end hardware and are willing to spend the $ to stay current. The question is whether it's worth it to you. If you are in a situation where money is no issue, by all means get the best machine you can right now. If money is tight, or you're not really a hardcore user/gamer, or if you just don't care and you're happy with what you have, then s tick with it.
Yes your computer is outdated. Is it obsolete? Only you can answer that. Whether you need to make a change is entirely your choice."It's only obsolete when it doesn't do what you want it to do any more"
BTW I hope you aren't running Win XP which was still a viable choice when you built that machine. Support has ended and you are very vulnerable to exploits, attacks, etc with that OS. Please use Win 7/8.1/10
Mackerel sums it up well. If you find yourself unable to run apps/games smoothly, maybe it's time to upgrade. But, if you are able to use the PC well for what you bought it for, then don't upgrade for the sake of upgrading.
I get this feeling from time to time as well since I haven't upgraded since purchasing the 4770K way back when they were released, but my PC is still able to run every application I use it for, and does it well, so I've managed to not upgrade the computer.
(I did replace the 39" Seiki monitor with a 43" LG though)
Upgrading a Haswell machine doesn't make sense. 1st/2nd gen Core i, sure, but haswell? Nah. You're good for years.
