TLDR: Great game, dated graphics, horrible bugs/glitches in this version. I recommend playing the original.
The benefits in this version are mostly water effects, slight lightning improvements, enemy ragdolling and easier object pulling/pushing. Most of the disadvantages are listed below.
The story is simple and the game's got many weird elements compared to the current FPS's, but it's still a great game and a classic. Looks like it takes like 9 hours to complete when you loot every place, but know where to go and what to do.
To list a of a few really annoying or game breaking things, many compared to original Half-Life:
-HITBOX/HIT REGISTERING PROBLEMS!
-The blast pit monster doesn't do damage to you or the security guard who's supposed to die.
-The leeches have almost non existent hitbox.
-The helicopter doesn't seem to register hits from gauss or RPG (didn't get it to even smoke).
-The gonarch or whatever has a crappy hit registering.
-The final boss has a crappy hitbox (I have beaten him in normal half-life with hard difficulty many times and this was 5 times harder in easy difficulty)
-HORRIBLE VISUAL ARTIFACTS in "residue processing" and somewhere else too.
-NPCs go "YAARRG" every 0.5 seconds if they are damaged.
-The crowbar makes a metal hitting sound when you hit any object and so gets really irritating when destroying boxes.
-The boxes take more time to break with crowbar, which adds to the previous annoyance.
-You jump higher than you should (IE You can jump crouch straight on top of a box in the laser tripmine building)
-The barnacles lower their tongue really slowly, but they can catch you when their tongue isn't lowered yet. This leads to some funny scary moments though.
-Missing dialog/AI problems.
And if you're new to Half-Life (and don't know whats supposed to happen or where to go):
-You can jump crouch above one vent in "we've got hostiles" vent maze section, get behind a fence and get stuck in an area you've been before (your auto saves will get replaced by the being stuck ones too).
-You see only blackness through the dam turbines, which has lead people to think it's not the right way and get stuck.
-You can shoot the scientist through the glass in "apprehension" and the game doesn't end, so you can't get the door open.
-The missing dialog/AI problems can really confuse you.
If you're hard-core and want the authentic Half-Life experience, buy the cds and patch the game to 18.104.22.168, cause the steam "original" version is bugged in many ways too nowadays. I would actually say that this Source version has better working AI in general than the other steam version.