Dean Takahashi wrote an article about Space Marine and how it's ripping off Gears of War. You should probably go ahead and read it.
 
I've gone through his article (now updated, btw) and tried to pick out all his arguments. He claims that he's just talking about the video games themselves and the gameplay, not the actual universes. We'll see what valid arguments there are. Mind you, I'm not even a fan of Warhammer 40k, I've never played the tabletop game or bought a single sourcebook. I was always just a BattleTech fan. But even I can see this is retarded.

He says:

-Grunts in GoW are copied from the US Marine Corps, and Space Marine is copying GoW.
-Both games have oversized armor and body-builder physiques.
-Both games have a large target reticle, so Space Marine is copying GoW.
-Guns are huge and you can have a chainsaw blade, just like the chainsaw bayonet from GoW.
-Blood spatters are similar.
-Guns shoot in a similar fashion.
-Space Marine has a thunder hammer, just like the gravity hammer from Halo.

The first one is about how the characters in both games are derivative of marines in the US Marine Corps. Well, I'm not sure what this has to do with actual gaming. It seems like a story or lore element, doesn't it? Doesn't factor into the gameplay of either game. The Space Marines came much earlier, and they've always been portrayed as meatheaded hyperaggressive soldiers, so... yeah, no copying from GoW here.

The second argument is that visually, Space Marines have oversized armor and bodybuilder physiques, just like in GoW. Again, not really a factor of gameplay, it's purely an art aesthetic of the universe, created back in 1987. They've always looked like this.

Both games have large target reticules. Now, this is certainly in the realm of video games, there's nothing in the universe of WH40k that specifies a specific reticule size. I haven't seen any gameplay video of Space Marine that actually shows the HUD, so I guess I'll accept his word that the game has a large reticule. Large reticules in third person shooters apparently all come from the Gears of War games.

He also argues that both games are similar because they have large guns and a chainsaw-like melee weapon. Well, the large guns visually are just another aesthetic of the universe, so that doesn't have anything to do with the gameplay. The chainsaw-like melee weapon is a gameplay component however, so let's take a look at this. In GoW, you can rev up the bottom of the gun and chainsaw people with it, one at a time. The chainsword in Space Marine is a melee weapon that allows you to perform lots of fluid sword slashes to quickly slaughter multiple enemies. While the chainsaw bayonet is rather slow and only works one on one, being completely ineffective against an entire horde at once, the chainsword is shown to be quick enough to slice and dice between multiple targets in close succession. It feels like much more of a dedicated melee weapon, while the bayonet is more of an afterthought. Of course, it's also different in that it's a sword and not connected to any gun at all, which limits you to melee only. And it's been part of the lore and tabletop game since the very beginning. So... yeah, I don't think this is them copying GoW.

Blood spatters are similar in both games. Well, this is kinda vague. It's true, both games have blood spatter, and they seem similar. There's nothing in the WH40k universe that says much about blood spatter, except that it exists. We can chalk this up as a strong visual element of video games.

Guns shoot in a similar fashion in both games. I'm not even sure what this means, other then that both games have guns that shoot bullets towards the center of the screen? And there's recoil involved? You shoot the gun, and then feel some recoil from shooting the gun? Is that what he means by guns shoot in a similar fashion? Well, shooting is an important aspect of any third person shooter, so yeah, it's a video game argument. You also do shoot from a behind the shoulder perspective in both games, though GoW didn't come up with that, Resident Evil 4 did.

Finally, Space Marine's thunder hammer is a lot like the gravity hammer in Halo. Well, first of all, it should be noted that Halo is a first person shooter. Dean seemed to be comparing the similarities of Space Marine and GoW as third person shooters. First person shooters aren't generally known for their melee combat, so it seems hard to compare it with the third person melee-centric gameplay of Space Marine. The thunder hammer also came from the universe of WH40k, back before Halo was created. I think the existence of the hammer and its use as a melee weapon is due to the lore and universe, and not the copying of a gameplay element from Halo.

So... ultimately, the only real video game arguments he has are:

-Both games have a large target reticle, so Space Marine is copying GoW.
-Blood spatters are similar.
-Guns shoot in a similar fashion.

If Dean Takahashi is truly upset by Space Marine because of these three points, well... he needs to be criticizing a lot more development studios than just Relic.