Everything in the army list has it's place. The only thing that I think is not worth it in most battles is the Land Raider. This army does not have much that is really superior to the counterparts found in other forces. If you want to play an army list with units superior to their counterparts, play Eldar or Chaos or Guard or Tyranids, essentially everything but marines. Marines are like today's Special Operations units, good all around but the true masters of nothing.
Marines do have one unit that is vastly superior to everyone else's equivalent unit tactical squads.
The real killer combo for Marines is the six-man squad tactical squad. Give it a Lascannon, plasma gunner, and Veteran Sergeant with a power weapon and bolt pistol. Mount them in a Razorback with Lascannon, twin-linked plasma guns, smoke launchers and extra armor. They can become a dedicated shooting or assault unit depending on the army types you're facing. For a leader model I tend to like Commanders as my primary choice with Chaplains as a close second.