So what should I be looking at?
Well, strokes for folks, and if F1's your bag then you won't need any variety over there to enjoy it.
Ways you could approach Forza though...
1. A tuner. You can play around for ages trying to tweak and refine any given car's setup to get the most out of it
2. An artist. You can design different, um, designs, for cars, try and recreate classic things like stick the old red/green Castrol livery on the GT-Four etc... or stick Kirby all over every car you own
3. A photo/video-grapher. You can drive to scenic places and try and get nice artsy shots, or create videos of interesting races, or videos of anything. One thing I intended to do with F3 but never got around to was recruit someone else, go to that italian village track, just the two of us in a private multiplayer, have one car painted as a cop car, and film a chase movie
4. Car collector. By amassing credits either through world tour or competing online (love this aspect now, that online play rewards you), you can try to "own" all the cars you're interested in, if that's your bag (this aspect less important to me, after doing it in 1, 2 and 3...)
5. Standard single player campaign. You can try to clock the entire thing. I'm a bit of a perfectionist and like coming first in every single race, for example
6. Time trials. This is my particular favourite, trying to climb up the online roster. "Rivals" provides some nice dressing for this core activity, and there's so many different race modes, I could break this into further categories if I had time
7. Online racing. So easy if you're in a car club (such as the OcUK one), just go for live races in realtime with other people (less interested in this myself)
8. Autovista. Obviously the most expressly limited option, but you can spend a wee bit of time exploring the high detail models and listening to Clarkson
9. Driving skill. Just another aspect of time trials really, but negating the online aspect, just trying to be smoother and put in nicer laps. Trying to learn the physics.
10. Achievement whoring. As is usual these days, you can aim to collect all the badges/titles for your playercard.
Now maybe some/all of these don't interest you, but it's what I think of when I fire up Forza, as things I could do within it.