I wouldn't say Guardiola's teams are boring per say, but they play in such a way that leaves no jeopardy, which is what a lot people find boring. His teams don't play on the transition which slows the game down. Guardiola is in his Louis van Gaal phase now.
This reminds me of our Ajax team that played under Louis van Gaal. That team was called boring by a lot of us older Ajacied, especially those of us who saw the Rinus Michels, Ștefan Kovács and Johan Cruijff teams in the past. People found it seriously boring. Our wingers didn't take on men anymore. In fact, I have friends that cancelled their season tickets saying that the football put them to sleep.
One thing we must be careful of is using the way Manchester City play now, and superimposing it on the past playing styles of the Pep Guardiola's past teams.
His Barcelona in 08/09 is one of the most exciting teams I have seen in my lifetime. They played great transitional football because they had Messi, Eto'o and Thierry Henry as the front three and teams were not sitting back, so they didn't take as many positional "steps" towards goal. As teams started sitting deep, his teams had to be more methodical to break them down. Even then, at Bayern he played transitional football with Douglas Costa and Coman on the flanks. At Manchester City, he had Sane and Sterling, and if my memory serves me correctly, they were close to the top when it came to teams that scored from counter attacks in one of the past seasons. Please do correct me if I am wrong
Guardiola's football is extremely high risk which is very ironic considering that a lot of people seem to think he plays risk free football. We all know Pep Guardiola now wants his team to build in steps as they work their way the opposition goal, but is it his fault? If the opposition simply want to sit in and counter, should he not do what is best for his team to prevent counter attacks? We have seen the games when Liverpool and Manchester City go head to head and those have been some of the highest quality games. When teams do decide to go "toe to toe" with them, they are extremely good to watch. Is it perhaps their domination that is boring?
From a coaching perspective, his team is something that is hard to understand and explain. The difficulty to get a team to play that way cannot be overemphasised. From an observer that grew up watching Piet Keizer marauding down the flanks, I have definitely been more "entertained".