Wich game franchise next?

SS and DE are top of the PC platform line-up. TR series is just a mixed bag of quality, as older ones didn't aged well, while newer are sub-par to them (pre-reboot).

I'd say go for Deus Ex, there are multiple ways to complete missions (I prefer stealth but you can go full Rambo if you want, no restrictions) so you won't get bored fast by playing games from the same franchise.

well then youll find a good story on both SS and DE. but since i cant stand Deus Ex invisible wars just go with system shock.
And you could also play the fisrt bioshock if you havent before.

Deus Ex because it's friggin' awesome. It has a great story, awesome RPG mechanics like being able to hold any gun in your hands, but it being completely useless if you don't have at least the minimum level of specialization in the skill for using it), alternate paths to mission objectives, freedom of choice system(including whether you'll go about your mission in a lethal or non-lethal manner), as well as stealth game-play and decisions that influence the story. It also has interesting characters and good voice acting and features a very compelling and immersive cyber-punk universe. And you'll want to equip it with the Shifter mod cause it makes it a lot more interesting.

The second game lost a lot of the charm of the series, so I recommend skipping it and going straight for Human Revolution. It's a prequel to the first game and a damn good one at that. It has lost some of the hard-core RPG elements, like the gun specialization. Also, the computer, electronics and lock-picking skills have all been incorporated into one generic hacking mechanic(which is weird even from a story point of view, given that traditional doors with mechanical locks seemed to exist in the future, but not in the past, where they were all electronic) and melee weapons have all been replaced by a generic take-down mechanic, which has a nice cut-scene to it, but limits your choices greatly. It has, however, compensated the simplified mechanics by amping up the difficulty with better AI, making enemies a lot less susceptible to bullets in an open gun-fight, allowing them to wake up their downed, yet still alive(knocked out) friends and replacing the traditional light-shadow stealth system borrowed from Thief The Dark Project with a new one based on cover and breaking the line of sight, which isn't quite as overpowered. But it still retained a lot of the other core game-play elements of the original and managed to recreate the same feeling enough to be a much worthier addition to the series than Invisible War. And coupled with a story that actually surpasses the original, I'd say it's a very, very awesome game that should not be missed. And given that it's a prequel, you can even play it first.

i would hardly recommend monkey island.
when it comes to your suggestions i would say deus ex

Mass effect o_O

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"PS: Story is the most important part of a game Imho;)"
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You might try Gabriel Knight series or Thief series. If you haven't yet played System Shock and Deus ex then you still haven't experienced the greatest games of all time :D.

Look for System Shock portable. You can download it from someplace and it's optimized to run on new systems.

Elder Scrolls

Deus Ex, The Witcher, Crysis, Grand Theft Auto, Assassins' Creed, Treyarch's Call of Duty. Maybe you could try Sleeping Dogs and Dishonored, even if they are not franchises (for now).

System Shock 2 (SS2). It is considered the spiritual predecessor of the Bioshock series, hence the "---shock" suffix.
The game is revered, even today. Plot details: You are placed on a spaceship mysteriously over-run by monsters, and you must use your cybernetic/psychic powers (along with the usual repertoire of weapons) to overthrow them. You also have to find out what happened to the spaceship, and its crew. The story and atmosphere are second to none. You will make moral choices in the game, that determine your good/evil alignment. The gameplay is hybrid FPS/RPG; at first glance a first-person game, but you later can increase your stats as you progress, affecting the choice of weaponry/cybernetics available. Your stats also determine what you can access; you can open doors easily if you're hacking skill is high enough (to hack the electronic locks placed beside the doors), but on the other hand you can break the lock if you're strong enough. So there are multiple ways to progress, all adding to the depth of the game.

It is the first choice for me. Considered one of the best retro games on Steam for good reason....read the reviews and you'll believe me.

Deus Ex -- very similar to SS2 but inferior IMO -- comes a close second, followed by Tomb Raider in last place (a good game but not as groundbreaking as SS2 or Deus Ex).

BTW you don't need to play SS1 to enjoy the second game!