I wanted to make a quick reply, but noticed if I said one thing I had to explain a chain of thought for it to make sense.
I wouldn't call it cliff hanger. It was open ended. Cliffhanger would be if they left the characters hanging from a cliff and nothing else had been resolved. Which is what HL2 did.
This is true, but the problem wasn't JUST the fact it was a cliffhanger ending, it was the fact that they "really focused and cared about the story" but forgot to actually tie up any loose ends for Half-life 2, while HL1 was pretty much self contained, its ending, felt like an ending. HL2:EP2 did a MGS5 where it just fucking stopped.
Half-life 1 plot of "Get the fuck out of here", and "Close those fucking portals" where resolved. They where simple, but resolved. Gordon was left in limbo, but that was an accepted fate since he had done A, "Got the fuck out of there" and B, "Closed all those portals by killing space fetus". G-Man coming up to you say "all according to my plan" was just the cherry on top, but it didn't really matter. He was an exposition dump and a sequel hook, but you could remove him entirely and the ending with him with Gordon teleported outside with Barney and a few scientist and have them spout out things like "Oh shit you did it, now lets get the fuck out of here, I wonder if escaping government kill squads is something I can list as a skill, eh Gordon?".
To avoid making a really long rant about half-life 2 short comings, to put it short it did not resolve anything with maybe one or two exception. Gordon got shit moving, but you didn't see how anything got resolved. The plot was much different from "get the fuck out of here" plot HL1 had. HL2 had alien corporations and entire planet occupation plot which didn't really get resolved after killing Breen. You blew up a really big fucking building, and that was suppose to again stop the fucking portals from working. That what was implied at the end of HL2. Episodes 1 and 2 though said, yea, that didn't do shit, but please start fucking again, you can have babies again. Then they killed the black old plot device to making it seem important. The only thing Gordon did in HL2 was blow up an alien erection building that let everyone start fucking again, and before you could do the thing you wanted to do since the first damn game.
What happen with that occupation force? What happen with that rebellion? Is that alien fleet coming? Did everyone start fucking for more babies? Is Earth going to recover. Did the fucking portals stop? Did I Win?
Sure the game and gameplay is all there, and the plot is an excuse plot, but it attempted to have a story. If the gameplay sucked ass no one would give a damn thats for sure. However they wasted money on tech to make you "care about the characters" and got a writer to write a script, filled with crisis and conflict, and above all else, making that a fucking selling point. Hell it was on the back of the box. Fuck, it was part of its titles "Episode". They wanted people to care. Then they spent 10 years fucking off in a corner making hats.