Cons: Many of the best games are getting pretty expensive these days
The SNES featured a 16-bit processor based on the 65c816. This chip operated at a maximum speed of 3.58 MHz and could perform block memory transfers thanks to it's direct memory access. The video was tile and sprite based, and was handled by the Picture Processing Unit (RP2C02) -- an efficient little chip that only had 64 kB of SRAM. It could display over 32k colors on the screen at once and had a normal resolution of 256x224 pixels. The audio was processed by an 8-bit SPC700 and an 8-channel Digital Signal Processor, which shared 64 kB of RAM and generated 16-bit wave table sound. The console also contained 128 kB of DRAM, as well as a regional lock-out mechanism so that you couldn't play games from one region on a SNES from another.
The console itself is about 8" wide by 9.5" deep and 3" tall. Nintendo dropped the front-loading cartridge slot that the NES used in favor of a top-loading slot for the SNES, and it seems to have really helped make the console more reliable. While I've owned 6 or 7 NES systems over the years, I've only ever owned 2 SNES consoles and they both still work perfectly.
On the back of the console is "multi out" port that you can use with standard composite/RCA jacks, an RF out port to hook up the console via a coaxial cable (and a channel selection switch to be used in conjunction), as well as a port to plug in the power adapter. The very first SNES we owned had to be hooked up with the RF adapter because our television didn't have RCA jacks at the time. I don't recall if the adapter originally came with the SNES or if we had to purchase it separately, but eventually we got a new television and started using the RCA jacks instead because they provided better picture quality. Setup is pretty self-explanatory, and any monkey could hook it up.
The power and reset buttons that were on the front of the NES were also changed, and were relocated to the top of the console. Instead of buttons, they were also turned into switches that slide back and forth. Between the switches and the cartridge slot being located on the top instead of in the front, this made the SNES less convenient to sit down in the entertainment center like a VCR, so it often found itself setup on the floor instead. Sure, it may have helped keep the vents more open so the console collected less dust, but I always felt it was partially done on purpose so that your SNES would more often be placed in a more visible location instead of being shoved down in the entertainment center like everything else.
Now the games available for the system is what really compels you to pick it up, and the SNES was no slouch in that department. There are literally hundreds of games available for the system, and they cover a broad range of genres. Fans of role-playing games will easily find this to be best system of its era, maybe even of all time (though the original PlayStation is probably tied here). Square alone brought games like Secret of Mana, Secret of Evermore, Breath of Fire, Chrono Trigger and the Final Fantasy series exclusively to the SNES.
Platformers were also well represented by Super Mario World, Mega Man X, Donkey Kong Country and Super Metroid. While the Genesis did have the Sonic games, as well as a few good exclusive titles of its own (Shining Force, Gunstar Heroes, the Phantasy Star games), it was still hard pressed to compete with so many quality titles on the SNES. The Legend of Zelda: A Link to the Past, Super Mario Kart, F-Zero, Starfox... the SNES had no shortage of exclusive, quality titles. The Genesis did have an edge in sports games though, and the good exclusive titles it did have still made you want to own one.
The SNES did lose a little traction because of Nintendo's aggressive censorship policies at the time. This wasn't good for games like Mortal Kombat that relied heavily on the blood and gore as a main selling point, but Nintendo eventually stopped the practice.
The games all shipped on cartridges that were just over 5" wide, 3" tall and just under 1" deep. The cartridges can hold up to 64 Mbits of data, though I believe the biggest games like Star Ocean are only 48 Mbits. The most common size for SNES games is 8 Mbit, so there was plenty of room for larger and more complex games. These cartridges didn't seem to gunk up and need cleaned nearly as often as the old NES cartridges did, and in fact all of my original cartridges still work (though a couple have dead batteries, resulting in the SRAM being erased and my game saves no longer saving).
The SNES also supported enhancement chips inside of cartridges to act as co-processors. This was a huge boon for some games, as the relatively slow clocked SNES would not have been capable of playing some of them correctly and/or at full speed otherwise. The list of games that took advantage of this feature is not especially long, but a lot of them are really good games such as Starfox, Star Ocean, Super Mario RPG, Super Mario Kart and Mega Man X2/X3.
The controller is pretty iconic, and helped to influence controller design for just about every console that came after it. The directional pad on the left, start and select buttons in the middle, the four round buttons in a cross on the right (A, B, X and Y in this case), and finally topped off with a shoulder button on each side. The PlayStation, Xbox, and just about every other console can thank the SNES for the inspiration. There were also a couple of additional controllers, such as the Super Scope gun (which doesn't work with modern LCD or plasma televisions) or the SNES Mouse (which I received with my copy of Mario Paint). These were supported by a few games, but were mostly pointless.
These days it's getting harder and harder to find working SNES games, and some seem to be all-but-impossible or extremely expensive if they were not produced in sufficient quantities. A lot of my games I picked up used from video stores when they quit renting out SNES games, but I've also had decent luck at flea markets and the occasional yard sale. I've picked up a few online that I really wanted, but usually people online have some idea as to what the games are worth so you don't find the occasional killer deals that you can find in person.
Overall the SNES is a great system, and being a huge RPG fan I absolutely have to keep one on hand at all times. A lot of SNES games have since been released for the Gameboy Advance, Nintendo DS or on the Wii's Virtual Console, but many have not. I've seen used/refurbished SNES consoles for sale for as low as $20, and many of the games are only a few dollars each as well. Unfortunately some of the best games, the ones you really want to own, are going to be upward of $50 these days. To replace my copy of EarthBound for example (dead battery, a little scared to risk breaking it to desolder and solder a new one in), I could expect to pay upward of $150.
The SNES is definitely still worth picking up, and a number of wonderful games can be had for $10 or so each. Just be careful what you're getting yourself into if you start picking up some of the more expensive classics or trying to collect every game for the system, because it's going to add up mighty fast.