Hi - Just wanted to chime in with my (humble) opinion. I moved to the DC Metro area 7 years ago and have lived over on the VA side the whole time. During my short time I've noticed a lot of things change around here - some good, many worse. First of all, if you don't like traffic, stay far far away. It really is THAT BAD. It is quite a mix of cultures here - worldly even. You get diplomats from all over the world. But, I would say most people are always in a hurry, impatient, and rude. Also, the high concentration of "self important" people makes for some interesting encounters. You'll have a hard time breaking into a social circles if you aren't a mover and a shaker. Again, if people feel like you can advance their cause, they will happily befriend you. But the people overall seem quite distant - like one big cocktail party.
If you're not into the "college town" feel, do NOT go to Arlington! This is just a place for people who are graduated and continuing college life from their apartments and condos. Nothing like a 35-year old acting like it's still undergrad! Alexandria is a very large and diverse area. There are some wonderful parts with lots of history (Old Town) to flat-out crapshack holes (Rt 1 South). There are definite scary areas - just be careful. However, be forewarned that a condo in any of those areas (1 bedroom) will start at $300,000 and go up quickly. A 1900 sq ft townhouse with 3 bedrooms will start at $700k in a good location. For something more "affordable" you'll need to move further out. And then you'll be sitting on the "Park"Way - aka the Beltway/I-95/I-66. If you're > 20 miles out from DC, count on a 1-2 hour commute each way with traffic. It keeps getting worse too. VA refuses to do road improvements.
As for activities - there are endless activities. Anything you can think of. Of course, getting to the beach will take forever with traffic. Going to the Shenandoah is a great trip...if you can avoid traffic. DC itself is a very scenic city. I'd never live there though. Too much tax, crime is rampant, and housing costs are out of this world.
Personally, I'm trying to get away from here. Yes, there are job opportunities galore if you deal with the gov't or are in hi-tech. Salaries can be quite good if you work for a defense contractor. Overall, there seem to be endless jobs. But you also have to deal with all the newbies (myself included) who are trying to make their mark around here. It is cutthroat, dog eat dog. If you're ready for it, you'll love it. If you're not, it'll be a major shocker.