I have Vampire since forever on steam, but never played it. It is worth?
I'm also about 50% into Deus Ex:HR. So, should I keep playing that game... Or start Vampire?
Keep playing Deus Ex: HR. Finish up that first. Great game, BTW.
Vampire: Bloodlines is fantastic. My favorite game of all time.
If you like those old-school RPG/action games (in which your stats & skills mattered and dictate how well or poorly you attack and if you can handle dice-rolls) before Mass Effect 2 was the game-changer - you owe it to yourself to play Bloodlines. It reminds of the original Deus Ex in many ways, as you could approach quests in many ways (i.e. enter a vent or somewhere and play stealthy; or go head-on through front-door and attack-crazy; or mix styles; or whatever), even if the final result is the same place. Though, sometimes you also can have different decisions with different outcomes from some quests in Bloodlines, as well.
Also, if you appreciate great storytelling, narrative, Lore, atmosphere, licensed music, traditional-style scored music (from Womb Music), and level design - you definitely should play Bloodlines. Some of my favorite quest-strings and actual levels are in this game. The Haunted House level is one of my favorite game-levels of all time. Not many games and/or levels can get me creepy out, scared, or on edge - but this one did it for me. Also, the whole ordeals w/ the two sisters Therese and Jeannette running the Asylum nightclub is one of my favorite quest-lines/quest-strings of all time; especially w/ the final part of that storyline; fantastic and jaw-dropping.
Make sure you grab one of the Unofficial Patches, whether you pick Wesp's Unofficial Patch or Tessera's True Patch...or else likely the game won't boot up b/c it won't recognize how much RAM you have properly; their patches fix that issue right out-the-gate. If you are doing a first playthrough, I'd recommend either Wesp's Basic version of his Unofficial patch or Tess's True Patch as those basically mostly fix bugs and maybe change a few things. If you want restored content, major changes, and/or anything else - then you should take on Wesp's Plus version of his Unofficial Patch or go find some other mods that are out there.
On Playthrough 1, make sure you don't play as a Malkavian. They have their own lingo and are hard to understand what they mean, unless you already understand the storyline, plot, and whatnot; and played through the game once already. Malkavians are crazy - so they can talk to Stop Signs and other inanimate objects; and also hear voices from out of nowhere. So, yeah - save them for a replay.
In the 1st 2/3rds of the game, if you want a Speech-based character - yeah, you can get through a good deal of that part of the game with little to almost no combat. But, in the last 1/3rd after the big decision-making cab ride - you better have already sunk some points into action-based skills (i.e. melee, guns, etc) b/c the game gets much tougher in the last 1/3rd and is very action-heavy.
Play 'em both. Both Deus Ex: HR and Vampire: Bloodlines are great.