Yep, this one is nicely made though portal kind of lacks enough plot to do a proper movie without combining both parts and changing the story and I hate when adaptations change the plot.
Hmm, it could go starting with the story of portal 1, then the time skip filled with the ratman and his flashback and then portal 2 story. Could work.
There is soooo much more to portal than the games (considering it's set in the hl universe). It could super easily be made a movie. Hell, you could make an entire movie about borealis.