They all deserve critical acclaim but I disagree with the majority in thinking that Halo: Combat Evolved was the best haha. Sometimes it simplicity was dull in my opinion especially when it came to level design. I think Halo 2 showed a developmentally better game than the original although had a weird storyline coming from the first. Halo 3 was a great game, although same issue with the second is the story line was rather weird. ODST was easily the best story line out of all of them to me. Never played Halo Wars though.
So yes I think all of them deserve their praise as they are beautifully crafted and designed games but I do disagree on some terms with how they are ranked intra-series wise as I think Halo: Combat Evolved gets a little more credit than it might deserve. But i was the first so I guess it does deserve it do to that "wow-factor" it brought in.
