All I hear about it is that it doesn't follow the Unix philosophy of a program should do one thing and do it well. And while it does seem quite large and do a lot of things, out of all the times I have broken my system, systemd has never been to blame.
I personally do not like that systemd gets more and more integrated with other software. For example Gnome. That makes it harder to use that software on non systemd linux, or other OS.