Longtime GTPlanet memebers may know how I feel about this. When I did my video on Ferrari on YouTube, I made notes that it's good to see a car company like this in the game, but don't be overly surprised. Many people just base good racing games only on the cars that are featured and almost totally disregard the actual game itself. "Driving Emotion Type-S" was an example of a game that featured some big-name companies (namely Ferrari and Porsche), but the game itself wasn't all that good or as well-liked.
As for Lamborghini's inclusion into GT5, I'm excited. It means that GT5's car lineup has a lot more character featuring some big-name car companies. It also means that it's something to look forward to if you're a fan of such companies. What I do NOT recommend is to call this game as the best in the series just because of a certain make featured. It doesn't matter what cars show up- a game can still be crappy even if it has the best cars that almost everybody loves. This is one reason why many love Forza more than Gran Turismo (among other reasons)- cars people actually care about. Like it's a waste of time being around kei cars and decent sports cars. Some GT fans cried bloody murder just because GT4 didn't have the automakers Forza included. If you're in this crowd, at least news of Lamborghini in GT5 equalizes itself and the Forza series on the front of cars people care about.
I think many people are just going to be on the notion of "finally! This car company is in the GT series!" Either that, or it's more like... "I'm not excited unless I can totally eviscerate the daylights out of this car with intense damage." I'm excited to get to know that I can race Lamborghinis in GT5. However, unlike most people, I also care about every other kind of car ranging from the Fiat 500R to a Honda Civic to whatever else we get on the sports car and supercar realm. From a non-fanboyish stance, I've voted "This is pretty cool. The more cars, the better." Sound and handling dynamics are still two key concern areas to me in regards to Lamborghini and any other car featured. Still, it's Lamborghini, people! Get excited!!!