I have no idea whatsoever so I'll just post the first thing coming to my mind seeing this drawing.
Eeeee... Rayman?

A swing and a miss. The first drawing could be pretty much anything but this next drawing will probably remove most of the ambiguity. If it's enough to make someone guess right... that's another matter entirely.

Krush, Kill N Destroy?

No, and I wonder why the second pic would make you think that, tho' I haven't played much of KKnD yet.

Sid Meier's Pirates although my other guess would be Anno 1602? Although I am wondering about the Giant Crab Monster.

It was crabs in it, and is isometric like your first drawing. Uh, I can't think of anymore yet ^^

I see... I didn't play enough KKnD to meet them crabs. But you are wrong in the assumption of it being an isometric game. That's just how I had it drawn.

It looks like another hint could be useful so here it goes: This game is older than the travels of Marty McFly.

Older than the travels of Marty McFly? So it's Pre-1985? Hmm... I will have to have another look at those drawings then.

damn you Elders of the internet! I had no chance to guess it then...

Well it's old and has crabs... the original Mario Bros?

Hah, likewise. I'll try with Dig Dug II, idk.

meh! If we are shooting here I'll go for sth outside a box... so... Crab Grab?

Curious! I imagined your crab drawing to be Reus, but this clue makes it kind of a puzzle.

Travels of Marty McFly, so release date is prior to 1985, I think. Unless, there's some other way to interpret that clue.

Updated version of the first pic. It was supposed to be like this the first time but somehow I forgot to put those details in.

I think this will be enough for the smart folks in this thread but if not I'll have another drawing by tomorrow's night of which I'm sure it will be guessed within seconds.