Let me start by saying the best quality that the area has (and most of the surrounding area, for that matter) is the cost of living. It is as great as everyone says it is. After saying that, if you like to eat out and shop, the Lewisville (and DFW) area is for you. There are tons of places to eat, mostly chain restaurants, but quite a few places that aren't. And the DFW area is overrun with massive malls and plenty of shopping.
Aside from that, nearly everyone drives horrendously bad (the worst thing I hate about this area), has a huge Truck or SUV, and is overweight. Lewisville Lake is one of the deadliest lakes in the nation because the boating habits are as bad as the driving habits it seems. Check out a map sometime so you can see how Interstate 35 runs through Denton, Dallas (35E), Fort Worth (35W), Waco, Austin, and San Antonio. Just try to imagine how much traffic runs along 35, with the overwhelming amount of cargo carrying trucks and poor public transportation (though it is slowly getting better). Needless to say, there is a ridiculous amount of traffic, especially in Austin (which is in the middle of it all), so it is truly no wonder that people drive so insanely. Being that I'm from near Chicago, and most of my family still is, I've spent a good amount of time driving on I-88 and other highways in the suburbs, and driving on 35 for the first time was unbelievable, it was like driving in downtown Chicago. It's horrendous.
That said, we live near 3040 on the south side of Lewisville, and it is really bad, and pretty much on par with Main St.
As far as the population goes, the area has been one of the fastest growing in the nation in recent years, and it really shows. The road construction is always well behind the the residential and commercial construction. The newest clustered mess is in Flower Mound on 2499 and 407. Old Lewisville (east of 35 on Main st.) is being slowly renovated in preparation for the new DCTA (Denton County Transit Authority) rail system that will link up with the DART rail system (they are aiming for 2012), and will run along 35E into Dallas (finally...), but it's still pretty shabby. Other than that, most of the area near 35E and Main st. is largely low-income and Hispanic, and most of the more affluent people have moved towards Flower Mound, Coppell, and Double Oak over the years.
As far as health and recreation go, the DFW area in general is terrible. There are very few parks, many of which are poorly kept up with. There are especially few in the Lewisville area. And as far as public recreation centers go, there are VERY few good ones, most people just get Lifetime or LA Fitness memberships (which are ridiculously expensive for recreation, and that's why everyone is in such poor health). The facilities are either non-existant, or there just isn't much too them, and usually dominated by kids programs (which hardly any kids in the area go to anyway, but in case one kid shows up, the facilities are closed). I have scoured the entire Dallas area north of downtown (not brave enough to go to the South side), and found almost no decent parks and no decent recreation centers (that includes Richardson, Garland, Plano, Carrollton, Coppell, Lewisville, Flower Mound, Denton, the Lake Cities, etc.). So believe me, I know. I am an avid disc golfer (obviously not since I moved to the area), and love to play pick-up basketball. Your best bet for the Lewisville area is the Farmer's Branch Recreation Center. It is the best Recreation center I have found. As far as park's go, Lewisville basically has 2 that I would consider parks. One is on the east side of 35 off of 407 near the golf course (Lewisville Lake Park). It is drunken redneck paradise, don't go there. And one of the best parks in the area (and it's only decent, and small) is Leonard L. Woods park. Every other park in Lewisville/Flower Mound is a patch of grass with a small children's playset, not a park.
Be prepared to drive to all those parks if you don't live right by them (and there are few actual "parks" to live by), because the area, as a whole, is certainly not walking or cycling friendly. The larger neighborhoods are great for walking or cycling (as most are), but there is nothing you can actually get to outside of the local neighborhoods. There are massive roads, and everything is very spread out, and the roads are very dangerous to cross. If you are looking for a more walking friendly city, I would suggest Coppell. I notice a lot more people walking in that city, and there are new and very nice cross walks there.
Even though there isn't much of a support for them, there are several cycling enthusiasts that live in the Western Flower Mound and Double Oak area. I think it's great that they pursue their interests even without a supportive environment, but to say they aren't truly risking their lives would be a lie. No bike lanes, mixed with exceptionally bad drivers is a recipe for disaster.
As far as politics go, I'm pretty open to people having their own opinions. You will inevitable run into your fair share of religious fanatics in the area, which might be a good or bad thing to you (I am, again, indifferent), they are usually nice, only a few are typically annoying. Most people in the area are generally pretty nice, except when it comes to driving. But most people in the area are commuters anyway, so most of their time is spent driving in a car, so you won't interact with people very often, which is one of the big reasons I want to move out of the area. Whenever I make a friend in this area through common interests or work, they end up living 30min or more driving time away from me.
The schools here should be much better, considering the funding they receive, but they are still seriously lagging behind. I blame the state government for allowing the schools to fall so far behind, but this state government has been pretty well known for dropping the ball on several occasions (their priorities seem often misplaced, and it seems impossible to get any incumbents out of office, unless they do something really awful). I'm probably not the best source on this subject, so you would probably want to look at some statistics.
Needless to say, I am dissatisfied with the area, and plan to move as soon as I am able (from the state entirely, in fact). Hopefully it will either confirm my suspicions of the area, or make me appreciate it more.