Dirty Ape, even a lot of Valve fans sort of agree with you on Episode 1. Main problem was, they kept introducing more elements to the game, but never gave you any chance to have real fun with them. Combat was too sparse, and the game wasn't as intense as HL2. However, check out the Metacritic comparison of Episodes 1 and 2...
http://www.metacritic.com/games/platforms/pc/halflife2episodeone?q=Half-Life (87)
http://www.metacritic.com/games/platforms/pc/halflife2episode2?q=Half-Life (92)
I have to agree with the reviews; Episode 2's major graphical changes, highly increased combat areas, extra length, and finally REVEALING a few things about the HL plot make it well worth it.
Valve's individual games are a bit too small to sell on their own, and they realize that everyone has one or two games in the pack they don't care about, or even just one or two they DO care about. So they priced the package at about 2 of their new-release games ($30 + $20 or so)
HL2 and Episode 1 are basically extras; when you look at the pricing, $50 is still a good deal if it was just the three new games. I suppose if you just want one game though, it's not as good a deal.