Following up the funniest comedy of all time was always going to (a) take a while and (b) be heavily scrutinized when it did eventually find a release. Dumb and Dumber resonated with audiences 20 years ago and remains endlessly re-watchable and quotable to this day. The pickle the returning Farrelly Brothers find themselves in is to have the humour evolve or not in a comedy world much changed since 1994.
For better or worse they don't; Harry and Lloyd haven't changed one damn bit and are all the funnier for it.
If you've seen the trailers you'll know that the film kicks off with Lloyd finally giving the punchline to a 20 odd year gag on Harry, where he pretends to have had some sort of mental breakdown. If you laugh from there then you're on board. The lads soon discover that Harry has a daughter, who now has a rich, intellectually revered adoptive father, and set about attempting to find her so she can give a sick Harry a kidney. And because Lloyd wants to shag her.
Just like the first film, Dumb and Dumber To knows exactly what it is. It doesn't for a moment try to give our leads any form of character arc, or mimic the more trendy comic leanings of the Judd Apatow crew; instead these are the same two morons doing the same stupid shit and it's still funny. Naturally, this is provided you found the first film funny...
It pushes the boundaries of a relatively congenial rating on numerous occasions as an up for it Jim Carrey and Jeff Daniels throw caution to the wind and embrace the ridiculousness again. They're obviously having a good time and it shows.
Such is the volume of gags that some do invariably fall a little flat, despite the commitment from its stars. And while there are many moments that will raise considerably more than a chuckle, there are no humdingers with the same level of impact as the '94 classic.
Lower your expectations, and, provided you enjoyed the first, fun will be had.