The reaction to MvC3's roster, especially the final one, was largely positive. People praised the inclusion of She-Hulk and Wesker while noting series mainstays like Akuma and weirdos like Hsien-ko and Super Skrull alongside other new characters that looked promising like Taskmaster and Dormammu.
As for MvC3's initial reveal people were very happy to see Dante and how cool he looked along with Deadpool. Capcom themselves mentioned that they put a ton of work into those two characters and it really showed and people were really impressed. What also helped were the absolute god-tier trailers.
UMvC3's reveals were also met with similar praise. People were excited to see every character on the list, even Nemesis. The fact that both MvC3 and UMvC3's rosters were leaked actually didn't affect the hype, if anything it increased the curiosity around them.