It has game of the year in the title for a reason, but if you are still not convinced , well I dunno.
This game is a gem of its time it's not a fps its a rpg with fps elements.
During your game you make a build would it be sniper man , pistol man, flamethrower mass genocide man etc.

I dunno, I like it and any time someone tells me their eyes bleed due to old grophics I can't understand them because the game looks fine.

PRO TIP SECTION:

game will probably not launch on win10 so use kenties launcher widescreen and all that nice stuff http://kentie.net/article/dxguide/

mods to consider playing after the main game would be:

Revision : On steam with chevos and coop survival and bunch of other stuff altho poor performance in some spots.

GMDX v9 : You can find it on mod DB, tries to stay more vanilla unlike Revision, but changes the gameplay ALOT more than revision does.

The 2 mods are for the most part vanilla+ if you ever decide to replay the game.

The Nameless mod : A standalone story mod that turns a forum into a very very well made mod with hours of content Evil,Good and very Evil paths in the story . One problem that some people might not like the humour, I love it, but I am also insane in the membrane. I still urge you to try it anyway.