Well I am gonna throw some oil on this fire.
Play the first one, whilst the storyline is fairly simple it is a vastly better game to the second ones. The setting may feel contained but it doesn't feel like you are simply checking boxes or just doing levels.
HL2 may have been genius at the time of launch, although I would debate that it suffers from clicheitus.
Driving section: Check
Zombie limited ammo section: Check
Different driving section: Check
Section where your character loses all weapons for no real reason: Check
Section were you have to fight off retarded AI whilst teamed up with even dumber AI: Check
Section were you are outnumber and out gunned and require pure luck to win: Check
Everything in HL2 felt segmented, for this section you will do this and for this section you will do that, were as HL1 actually felt like you were naturally progressing through the Black Mesa base and HL1 had some seriously good set pieces. The Blast Pit is a good example, yes effectively it was no different to the doom levels where you had to collect three different keys to complete the level but it was done in such an integrated way to your environment that it worked beautifully. There is nothing like that 'level' in HL2.
Okay the downside to HL1 is that you have to spend some time on the alien homeworld which is a bit... meh but it is such a small section of the game compared to the rest that it is forgivable. On the other hand the zombie hordes sections that appear in HL2 are just tedious and zero fun and are the primary reason why I dropped HL2 Ep1, once I hit yet another, you trapped with Zombies with limited ammo, section I just decided that the game was too tedious and too cliched to be worth continuing on.