Unreal Anthology is FPS paradise for $20.
Most PC owners don't have high powered rigs, so older titles that don't require alotta resources would be quite appealing to the mass market. Many gamers are already familiar with these franchises (Unreal, Counter Strike, Quake, etc...), so having them in a cheap box set will appeal to them. These titles, themselves, cost nothing to develop because they're already there. The only real costs are marketing (easy, considering they've got established fan bases) and distribution....quick money. And, of course, there's the games themselves.
The clear star of Unreal Anthology is 'Unreal Tournament 2004' and is worth the $20 by itself. The original 'Unreal Tournament' (released in 1999) is pretty cool for Old School heads. And yes, both of the "tournament" titles include bots for those whom play offline. I don't have to delve into details; you know how much they rock.
Unreal and Unreal 2: The Awakening are nice additions, but won't make any converts. But given this IS an "Anthology", it makes sense to include them. The fact that these two games are story driven give the collection some meat.
All-in-all, this is one of those box sets that I wish the industry would bring us more of.