His previous outings in Meet the Parents and subsequent sequels definitely place him better as Mob Bad guys that laughable dad's and although he is loved my many in these roles, for me it just bordered on cringe worthy.
The other thing is don't think that this comedy - The big Wedding is kiddie friendly - although the 15 certificate gives this away its the language that should keep fun loving parents kids far away as De Niro dropping a "C" bomb in polite conversation is only part of the barrage of curses bestowed upon the audience which for some may be too much but for me - were the saving grace of this movie.
Throw into the mix De Niro's long time girlfriend (Sarandon) who now has to dumb down her role as Step-parent to the kids, and as one time best friend to De Niro's wife (I am sure you can imagine what happened there) you can only presume that their long standing feud could reach fever pitch. Then there are the other two grown up kids (Heigl & Grace) offering their humorous quips that "it'll never work" and you end up with a very grown up affair.
I shouldn't moan too much - there were certainly plenty of laugh out loud moments and De Niro as the wealthy sculptor / swear box husband certainly out does his performances of other comedies he's been in. Sarandon steal the show as the adulteress and sexy girlfriend - offering a slightly bitter approach to being side-lined as after all - she has raised Alejandro (Barnes) from a child / teenager.
Wrap all of this up and there is enough story and sub plot to make quite an amusing flick - and although the leading role falls to De Niro himself - there is plenty else going on to distract you from the fact that when all is said and done - comedies still aren't his strong point. Everyone else however (mainly Sarandon & Heigl) are Brilliant.