I wanted to explain the Nexus Mod Manager to you, seeing that you picked up Fallout 3 & Oblivion. Skyrim, if you choose to get it and I HIGHLY recommend it, will benefit the most. Bethesda games can really flourish with mods.
Primer: nexusmods.com is a place for user created mods for many games, but mostly for Fallout 3 & New Vegas, Oblivion, and Skyrim. Once there, register and download the Nexus Mod Manager. It will find your games that it supports. Once done, when you find a mod you wish to download, you will have the option to "Download with NMM". One click and it will download. One more click, and it will install it automatically, and remove remove a mod as well.
Important: with Fallout 3, Fallout New Vegas, Oblivion, and Skyrim, always install these games outside of the Windows\Program Files folder. For example, I made a folder C:\Games and install my games there. Windows screws with these games and can cause issues, particularly when modding.
If I recall correctly, most Fallout 3 mods must be installed manually, but the NMM has really gotten better at supporting mods for the 'automatic' option. But for Oblivion, which is really what I wanted to talk about, there's one big thing you need to know:
Efficient leveling.
http://www.uesp.net/wiki/Oblivion:Efficient_Leveling
BTW, that site is the best wiki site for Elder Scrolls games.
The leveling system sucks. It's great if you learn it and follow it, but if you just jump in and play it like any old rpg game, the game will get impossibly hard, very fast. And I do mean impossibly hard. So, to remedy this, there is a mod to play it like a normal game. It's called "Oblivion XP". My version is 4.1.5. I highly recommend it. With EL, I literally made a spreadsheet to keep up with leveling stuff. Boo! I'd rather play, not chart skills.
Also, there is Qarls Texture pack III, which really helps in the graphic department. There are some others, but if you look under the most popular mods for the game, you'll find what you need. It's always fun to sift through the various mods. You can spend a lot of time modding your game to your desire!