I'm looking for games that don't require too much time to progress, but have good replay value.
I don't have time to play games which require hours and hours of grind, like Septerra Core.
In FTL I can start a new game, advance fairly quick, and the game has great replay value.
What other games are like that?

You should try RE:IS then. It's a fair game, a lot of replayability, gaming sessions are not that long (you can even sort of leave the game inthe middle of things) and there is challenge if you want That,

Edit : I finished reading your post ; while RE:IS has been compared to FTL in some circles, I find it superior. And it`s on gog of course (Renowned Explorers : international Society , or sumssin').

Depends how short a play time you're looking for.. Tales of Maj'Eyal is a roguelike, and therefore somewhat similar to FTL but a full play through would take a werk or two (though it takes a lot of trying, failing and dying ti get there) as opposed to the few hours it takes to get to the end of FTL.

Nuclear Throne, Downwell, Death Skid Marks, Convoy, Crypt of the necrodancer, Risk of Rain, etc.

Edit: I think it would be more easier to mention what kind of gameplay we're talking here, turn based, plataforms, shooter, etc?

Broforce :P

Vertical Drop Heroes?
Steamworld Dig?

It sounds like you're looking for arcade games. Or, at least, the arcade genre.
If you're talking about RPGs or something similar, however, I can't help you.

Edit: I second the recommendation of Downwell.

World of Goo is absolutely excellent and will keep you busy for a while

Tetris :-)

Rayman Origins is terrific in short bursts as well, and it has great replay value, otherwise I wouldn't have completely finished the game 3 times :P

Triple Town...
Ring Runner has arena and zombie modes, so those are short sessions to play...
Spelunker
Symphony
Race the sun
Olliolli
La-Mulana
Risk of rain
Din's Curse
Drox Operative
Luftrausers
Pixel Piracy
Crimsonland
Police Quest (I refer to the practice missions where you can do deciphering or other mini games)
The adventures of Shuggy

I'm not sure all of them are 'infinitely replayable' but there's a lot in most of them.

Rogue Legacy is probably the best. It's a lot like FTL, but as a platformer/RPG. Enter the randomly generated castle, fight monsters, die, use gold to improve your next character, and so on until you defeat all the bosses. Great fun, infinitely replayable, thanks not only to random levels, but every character having a unique mix of traits and skills.

Vertical Drop Heroes is a lot like it too, just even simpler and quicker.

Hotline Miami does not have such replay value I guess, but it's the fastest game you'll find. Very short, action packed levels, lightning fast gameplay.

Not a Hero also has short, action packed levels, and better replayability (extra objectives in every level for better ending to the game). I liked Hotline Miami more, but Not a Hero may suit your need better.

Risk of Rain! That thing is dangerously addicting... :)

Also, maybe you want to check out Tower of Guns, Hammerwatch, Ziggurat, Spelunky, Vertical Drop Heroes, Papers Please, Desktop Dungeons.

Crimzon Clover. An entire playthrough can be completed in about 45 minutes, and there is a training mode and a 3 minute time attack mode if you don't have time for that.

Of course, this game is a difficult bullet hell shooter, so it will take a while to get good enough to beat the game without using any continues.

I've tried to play some Touhou games and i'll agree to that...