Yeppo, Popsloader PS1 FF7. Its probably the one of the best games I have EVER played. Crisis Core is the story of the events that lead up to the Nibelheim incident which is referred to in FF7.
FF7 will fully satisfy your levelling, weapon collecting needs too. Also its a fantastic story. Won't look as good as Crisis Core but it doesn't matter. I played the game over and over again solidly for a year just for the joy of it all. Possibly one of the best games ever made, and had a legendary gameplay moment that happens at the end of the 1st CD. Its more RPGY than this, as in you get a bunch of characters and get to level them, the materia that you bind to them etc. You spend a good 3/4 hours just in Midgar at the beginning. Great stuff!
Final Fantasy 8 is also excellent, a bit more niggly to run (I've done a thread in this forum about it). Final Fantasy 9 is also really good and the best looking of the PSOne games.
Ok, materia. Materia are crystals which contain the knowledge of 'the ancients', which allow you to tap into abilities:
Green Materia - Magic, Attack, Restorative and Battle Buffs
Pink Materia - Permanent status effects in battle
Yellow Materia - Command abilities
Blue Materia - Effects (like scanning etc)
Red Materia - Summoning
Black Materia - dunno if this is in this game yet
You have 4 slots to start with to bolt materia onto. So you can go into battle with say Fire, Cure, Power Attack and HP+20% for example. When you hit SOLDIER 1st Class, you get 6 slots.
FF7's size... can't say it'll break 2GB. Maybe not even 1.5GB. Was just 3 CDs. The others in the series were 4CDs.
I appear to be quite nails in Crisis Core now. I really hit the side missions. Just had materia fusion unlocked so you can make your own. I've noticed that Fire/Blizzard/Thunder + Esuna = Dark Fire/Thunder/Blizzard.