Again though, to download a game on 360 don't you need an XBL subscription? And is the 360's online services even still running?

Nope and yes.

For how long the Xbox 360 service remains operational though remains to be seen. Xbox 360 games are having dwindling populations... So Microsoft may not see it financially viable to retain the 360 services over the long term, just like what happened with the Original Xbox.

The 360's servers are definitely dwindling but still active. I mean there are a bunch of notable games with active populations, the X1 has given a boost to those servers as well. Black Ops II is actually listed among the most played games on X1.

The original Xbox is a different story. It had a small userbase, a much smaller number of notable online games, and it was apparently hindering 360 improvements. 360 games are also an incentive to being a Gold user. Obviously there would be more fervor about 360 servers shutting down. For OG Xbox, I feel it was mostly Halo 2 fans that were upset.

PGR

Well. Some games are still active. Majority aren't. (In Oceania at-least, different geographical locations obviously have differences.)
But then again, allot of Xbox One games aren't very active either, like Halo Wars: Definitive Edition and Halo Wars 2.

And Microsoft can leverage the same argument against the Xbox 360 online services at some point.
It's not a matter of if they get shut down, but when.

Since im primarily a PC gamer games, like Kotor 1 and 2 doesn't count since they are better on PC (especially 2) i have to vote for Ninja Gaiden Black. Still to this day one of the best 3D action games and the only way to play it is on one of the Xbox consoles, most connivent being with the xbox one.

I think platform defining usually means either exclusives or titles that went unnoticed on other platforms but excelled on one, but I don't like most of the Fable, PGR (quite liked MSX on DC though), Conker, Blinx, Kotor stuff that is usually in the best of Xbox lists. So most of my favourites (Halo 1 not withstanding) probably aren't considered platform defining games but whatever.

Panzer Dragoon Orta was my favourite. I liked OutRun 2, Shenmue 2, Project Zero/Fatal Frame 1&2 ,Super Monkey Ball Deluxe, DOA2 Ultimate, Ninja Gaiden/Ninja Gaiden Black, Baldur's Gate 2, D&D Heroes, TimeSplitters 2/Future Perfect, Brute Force Jet Set Radio Future and Gun Valkyrie. I think I enjoyed Crimson Sea and Sega GT but I have very vague memories of those.

Most of these were available on other platforms and were sometimes better elsewhere. .

Never played Morrowind, Doom 3, or Half Life 2 on Xbox but I'd be interested too, probably decent versions but again not exactly Xbox defining titles since they were primarily released on PC. Lots of decent multiformat games had a port on the Xbox too.

Of course, mustn't forget DOAX Beach Volleyball

My favorite game on that system back in the day was Total Overdose, and Cars.

Most games do not have active online populations, that's expected and not exclusive to Xbox.

Yeah... no shit. We know there is a "when." Nobody is arguing the 360 servers will be up forever. I am pointing out large userbase, active games, streaming apps and BC might be keeping those servers running longer. 360 servers have also been up longer than OG Xbox servers ever were.

Backwards Compatibility however didn't exactly extend the Original Xbox servers. So I don't think that assertion really holds any real weight going by past precedents.

The Xbox 360 should naturally have a longer life line due to the fact it sold relatively well.