- Built-in DVD Player - Having a CD player in the PS1 was a nice convenience, but the DVD player in the PS2 was huge. For many people (my family included), the PS2 was our first DVD player and was the reason that we jumped ship from VHS tapes. At the time, the PS2 was a very affordable DVD player and it was a key factor in the success and wide adoption of the format. Hell, my younger brother has a PS2 and still uses it as a DVD player, which says a lot about the importance of this feature.
- Backwards Compatibility - Another major factor of the PS2's success is its backwards compatibility with both the hardware and software of the PS1. You could use PS1 controllers with no issues and PS1 memory cards could be used as well (although these memory cards only worked with PS1 games). The fact that you could carry over your collection to a new console generation made the transition more attractive and basically allowed the PS2 to immediately surpass its predecessor.
- Huge Graphical Improvement - The graphical leap between the PS1 and PS2 era was one of the biggest improvements of any console generation. PS1 games were very blocky and low resolution, but PS2 games were able to smooth things out and start to approximate realistic graphics. Hell, stylized games like Okami and Sly Cooper still look quite good to this day.
- 3D Gameplay Improvements - By the mid-to-late point in the PS2 era, developers were finally starting to get 3D gameplay under control. Camera issues still plagued a fair few games at the time, but gameplay was finally getting refined and control schemes were starting to become standardized in a manner familiar to the games that we play today. This, of course, makes PS2 games much more playable and easier to go back to today.
- High-Profile Exclusives and New IPs - Exclusives and new-IPs ruled the roost during the PS2 era, perhaps to a greater degree than in any other era since, making it a truly exciting time to be a PlayStation owner. Games like Metal Gear Solid 2 and 3, Ico, Shadow of the Colossus, God of War and Final Fantasy could only be played on the PS2, many of which were high-profile third party exclusives.
- My Favourite PS2 Games - Again, this isn't a comprehensive list of the best PS2 games (not by a long shot), but my favourite games of the era include: Splinter Cell (especially Chaos Theory), Metal Gear Solid 3: Snake Eater, Freedom Fighters, Star Wars: Battlefront I and II, Twisted Metal: Black, Shadow of the Colossus, Sly Cooper 1-3, Bully and James Bond 007: Everything or Nothing.
- Underpowered Hardware - I'm putting this under mixed because it didn't really matter, but the PS2 was clearly underpowered and missing features compared to its competition. This becomes very clear when you compare the PS2 port of Resident Evil 4 to the Gamecube original, or the PS2 ports of any of the Splinter Cell games to the Xbox originals. Still, the games worked and the PS2's impressive library basically made this a moot point, because the PS2's popularity made it the most successful console in history regardless.
- Legacy Hardware Issues - In many ways, the PS2 lives up to its name: it's a follow-up to the PS1, but the system itself doesn't make any major innovative leaps forward, a fact which really stands out when you look at its competition. For example, the Xbox was built around online gaming, whereas PS2 owners had to purchase a separate ethernet adapter which was expensive and under-utilized (although this did allow couch multiplayer to last for another generation at least). The Xbox also had a built-in HDD, making the necessary purchase of pitifully tiny, 8MB Memory Cards on the PS2 look embarrassing and archaic in comparison. A HDD was made available as an add-on, but it was once again an expensive, under-utilized peripheral which was only really used in Final Fantasy XI. The PS2 also had only two controller ports once again, making couch multiplayer games harder to manage.
- Glut of Shovelware - The PS2 era might have been the height of cheap, crappy licensed games, as they were very prevalent at the time, as this was an era where the install base was huge and games cost just enough to make that it was worth the investment to make a quick turn-around. In subsequent generations the mobile gaming scene would kill off this market trend (although it carried on over to the Wii as well), but when you go back to the PS2 you'll notice a plethora of awful games which were shovelled onto the system.