I love the SLS Black series, for a host of reasons: styling (hard to beat Gullwing doors), Mercedes heritage, rarity (300ish world wide, 130ish in US), normally aspirated 650 HP, etc.. At the moment, I have 2 of them. The only other time have had 2 of same car, is 2005-6 FGT.
It is however very different than a NGT or Senna. To me the SLS Black is more a superb grand tourer than race car.
The NGT and Senna to me are just all out track focused, uncompromising race cars, both of which are hard to believe are street legal. When you have to question a manufacturer's sanity for building a car such as the new GT (or Senna for that matter in my opinion), it says something.
If Senna wasn't $1m, and Mclarens didnt typically bomb in value, I would own one too.