It's old now but just to be sure - have you played the mod 'Research & Development'?
No, just started 'Call In'. Looked at R&D a while back, looked very puzzle based. I like killing things.
Yes, R&D revolves entirely around puzzles (although once or twice you kill things with the puzzles), so it feels a lot like Portal or the more claustrophobic parts of HL1.
It is the same quality of Valve's own games in terms of level design, humour and entertainment, though, so anyone who owns HL2 and doesn't mind puzzles should definitely check it out. Strongest recommendation.
Really enjoying this, reminds of HL1