Day of Defeat Source
I have played quite a few Online FPS games and mods over the years, most of the COD games, some of the battlefield games (currently bc2), and a lot of valve games.
But i always end up coming back to DoD:S
It's a shame the net coding is as typical as you can get for a valve game - you notice this particularly when you start to play Competitivley on ESL and other tourny platforms - you can optimise hit reg with a decent config and a good server but i have never seen an instance of probably more than 85% hit reg.
Other than that the multiplayer game play is so awesome and addictive! If valve did take a bit of time to realise that valve source games are still some of the most played games and attempted to really hammer out the issues with the source net coding they could stop some of the best online fps games from gradually dieing out!
I'm actually also playing another awesome valve source mod at the moment: Firearms source
http://www.firearms-source.com/its based on the original very popular Firearms Mod from the Half life one engine, an early version was installable from the HL1 disk in fact.
The game play is very fast and frantic - various updates have been made since its release in summer 2010 and its getting better and better, the weapons details and animations are simply some of the best - true to its roots - it was the same with the original!
Its a free mod so if you play source games you can download it and play for free
My other favourite game in the RTS group: Company of Heroes
Both a generally awesome WWII themed game and excellent online game play - loads of issues with regards to power balance and early/mid/late game advantages for various sides but they do try and fix these with every update (grrrr @ ROOS!!!!)
so yeah - some of my favs
^
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