Half-Life 1's major flaw is some slightly tedious level design, but overall this is still a masterpiece.
Half Life 2's major flaw is sporadic difficulty level. Sometimes it is pretty tricky but most of the time it is relatively easy.
The 30th episode to this epic series is out now!
or if you have never heard of it...here is the link to the debut of the series:
http://www.youtube.com/watch?v=7J80KD4BG7M&list=SL
:D
I am finishing up my first playthrough of half-life and dang surface tension is a long hard level. Incredibly long actually, but a ton of fun. Are later levels longer/harder?