Personally I find Karlovic and Isner game style as not real tennis. They definitely don't play tennis I like, but it would be silly not to call it tennis.
2 players who only rely on their serve and mostly winning points by ace or service winner is really boring for me to watch.
Still can't say its not tennis, but you definitely won't be far from truth if you say it has no tactic or any strategy.
99% of the time they just tank their opponents serve, only waiting to get their shiny-left-foot-by-the-baseline-
Now that I can understand someone doesn't like it.
But herc honestly, calling that short rallies don't involve tactics and strategy its just wrong. It takes actually much more strategy, considering almost every shot is forced error.
Now, why do I prefer short rallies? I enjoy watching aggressive players, and when they play on clay, most of the time they lose because they become very impatient on the long rallies causing A LOT OF UE's.