I think it feels short because of the linearity, and that there were fewer locations I think. Let's see, off the top of my head...

Besaid, Kilika, Luca, Mi'ihen Highroad, that battle site, Djose Highroad/Temple, Moonflow, Guadosalam, Thunder plains, Foresty place/ice temple, the desert, Calm Lands, Mt Gagazet, Zanarkand, Inside Sin (a few locations there)
Plus a couple of hidden areas from the airship.

I have a rubbish memory with names but think I got it approximately right

When you look at it, it seems a fair few locations. But then if you look at FF7's list...

Midgar (several areas, plus Shinra HQ), Kalm, Chocobo Ranch, Mithril mines, Condor fortress, Junon, Costa Del Sol, Corel Reactor area, Corel, Golden Saucer, Desert prison, Gongaga, Cosmo Canyon, Nibelheim, Rocket Town, Wutai, Ancient Temple, Ancient City, Icicle Town, Icicle Inn, Northern Crater part 1, that town with the lifestream lake, Northern Crater part 2, plus other minor areas, plus several hidden caves and things...

Yeah, FFX seems quite small in comparison. But it seems to last just as long.

FFXII in comparison... I haven't finished it yet (because it's dull) but I know I'm not far off the end and yet it's as if it's just started. The issue there is lots of places, but you just plough away fighting your way from one side to the other using pretty bridges and things, and there's not so much in the way of exploration (no specific hidden treasures, bah)