I bought into the hype and played this back in the day, but even without the crashes I found the possession mechanic to make absolutely no sense.

For example, I possessed a cop, then came across a scripted scene of some cops fighting some criminals (Chots or whatever they're called). I decided I would help the cops fight the criminals. I drew my gun and immediately all the criminals and all the cops turned on me and shot me. I hadn't even fired a shot, and not only did every criminal decide I was a higher priority target than the cops who were already shooting at them, but the cops themselves decided that I was enemy number one! I gave up on the game at that point and didn't go back to it.

Is the GOG version of the game still this broken?

I agree with you that the gameplay isn't really its strongpoint, still I like it because of its interesting premise its humour and one of the best depictions of a dystopian future I have seen .
The combat indeed boils down to a series of possesions/depossesions until you posses the last (wo)man standing but I thought it was rather hilarious to see them gunning each other down.
I believe the designers were threading some new grounds with this game and Messiah must be seen more as a gaming curiosity than as a gamers game imo.

Broken? You kiddin' me? There's zillions of games with that kind of issues and for some reason nobody gives a fuck unless it's Messiah because it's cool to hate this game for some reason. :P It's one of the earliest 3D stealth games, one of the few games that involve disguises and it's a game with different factions fighting each other. Back then lots of games had minor stealth passages and they pretty much always sucked (heck, even NOLF had terrible stealth mechanics a few years later despite depending largely on them), with Messiah Shiny actually went for a whole game based on disguise and stealth mechanics and it works most of the time - that such a small issue (which has NO meaning within the context of the whole game) is enough for you to give up on the game is ridiculous. What's next? Giving up on a GTA game because cops only hunt you but never NPCs?

If you're having crash issues, check out my thread: http://www.gog.com/forum/messiah/messiah_composite_quick_start_thread

Totally different kinds of stealth games, however. Those games are based on view and camouflage, Messiah like Hitman is basically based on disguises and stealth based on disguises is far more complex as that kind of stealth requires the AI to act accordingly to your behaviour in their view. And the fact that even the newer Hitman games still struggle with that mechanic, tolerating behaviour that should instantly turn them hostile or making enemies see through your disguise for behaving like the AI characters, just shows how complicated this kind of thing is. Especially the first Hitman, released the same year as Messiah, had strong issues of this kind and yet people seem to be far more forgiving in that case. And Messiah even has additionally factions which makes things even more complicated and justifies the occasional flaw in the system even more, IMO. (and yes, Hitman 1 officially does have factions but IIRC they never turn hostile towards each other ingame thus eliminating the issue you're criticizing about Messiah)

And well, in Messiah most of the time it's logical that NPCs turn hostile as soon as you draw your gun. Of course the developers should have introduced an exception to this rule when a combat situation between the factions arises but one of the reasons why they forgot / didn't manage to do this was most likely because there's so few situations where this would have been necessary and introducing this exception might have broken the basic mechanics. And the fact that you can still easily beat the whole game, despite this obvious flaw, is enough of a reason why you can't call the game itself broken. Well, it's illogical that AI controlled characters can do the same stuff as you do but the cops behave totally differently towards them (they can run over someone right in front of cops and the cops don't care, IIRC), basically the same thing you accuse Messiah of. Still I don't say that GTA is broken because of that. And sure, in GTA the issue is less obvious but I can't even honestly say that it's less harmful to the whole game. There's been quite a few situations in the GTA series where I failed a mission because for some reason the cops treat me much worse than anybody else in the universe. Yeah, I thought so. Oh well, I still liked it and always felt that it received too much criticism and will defend it for pretty much ever. Especially since it's one of the *very* few games based on disguises and the most original one at that (a cute cherub taking over people and wreaking havoc? awesome! :D).

I loved Messiah, but it certainly had its frustrating parts. In the world of video games, you'll find stupid shit like what you described happens all the time. It would be great if everything was perfect and worked the way we wanted it to, but such is life.

@OP. If you read one of the walkthrus available on gamefaq, you'll find you're not suppose to aim ANY weapon at all in a riot zone.

This cop killing cop (or chot killing chot) was fully intended in the riot zone. I guess the developers just didn't make it clear enough... Should have put it in one of those head-ringing messages prior to entering a riot zone.

The issue that really pisses me off about Messiah, though, is the incinerator last jump to the ledge. I could never get Bob to flap that high (had to use cheat to summon scientist and use chot helicopter gun to get additional lift)... Another issue that pisses me off was trying to break the bullet-proof glass (so you could enter a chamber) by firing at it. The developers didn't make it clear enough that you're suppose to throw a grenade at it... D'oh!

In short, other than the impossible jump to reach the last ledge in the incinerator, Messiah as a game has ZERO flaws in the code. The only flaws that exist are not being de-briefed about special circumstances, such as not aiming a weapon in a riot zone, or glass that can only be broken by a grenade...