I've actually played Roblox a bit just so I can make a video that's coming up, and the only game I think would be nice in Blockland would be
'Armored Patrol v6.3b' for two reasons;
It has quiet a selection of vehicles (Tanks, jeeps, Howitzer) and the animation is smooth, the shooting is crisp, and the gameplay is nice when ran with decent team leadership and such. If we had a Howitzer and some of those fancy things Roblox has, it would be swell.
And before you rage at me for saying Fancy, there are things Roblox has that Blockland would be cool with. You just have to look deeper then the "crap" you see on top.