Eitot: Why not simply be clearer? ‘Activate your Steam copy of LIMBO for free with GOG Connect’. ‘Connect your Steam library and import your copy of LIMBO with GOG Connect’.
Could be that they don't want to mention their direct competitor on the main page too loudly, as if advertising it. They have "hidden" the mention of the competing service to the instructions. If these hapless people saw Steam mentioned on the main page, it might even give them the wrong idea that GOG is selling/delivering Steam keys.
I think the banner is fine: it tells you can get an extra GOG copy of LIMBO with GOG Connect. If you don't know what GOG Connect is (ie. a way to get selected games from your Steam account to appear also on your GOG account), then that should become clear when you click on that banner.
Services like GOG Connect are a bit tricky to advertise right, so that you don't end up promoting the competing service. After all, we have seen also here some Steamheads snarkily commenting how it now makes even less sense to buy games on GOG (instead of Steam) because you can get the GOG copy "for free" anyway through GOG Connect. You know, like those "Great, another game for GOG Connect"-comments in the GOG game release threads.
I think that is also why these GOG Connect campaigns are only very limited time (during which you have to activate any eligible Steam games on GOG), and only for selected few games. Obviously the idea is not that people would end up buying their games on Steam in hopes of getting GOG versions for free on top of it, but a way to lure Steam people, who otherwise don't hang around too much on the GOG site, to come visit and check out the GOG site once in a while (if they care at all to receive a copy also on the GOG service).
CARRiON.FLOWERS: I remember trying to play this game after hearing all the hype and it boring the fuck out of me.
I normally don't care for 2D platformers anymore, but for some reason LIMBO was able to hold my attention when I played through it 2-3 years ago or so. It is not a long game, I think I started it one day and finished it the second day, same as with Portal (the Valve game), even though I am generally quite a slow player. I think the length of the game was fine, not too short.