It is a good university, with a wide variety of undergraduate, post-graduate, and doctoral programs. The university is known for research too. But, one reason people (namely International Students) may not consider it, is because the University's main campus is in North Oshawa in the Durham region with a satellite campus in Downtown Oshawa. The university is almost 70-75 km away from Downtown Toronto, making the commute far, unless you stay in Oshawa closer to the university or somewhere nearby in the Durham Region.
Commuting by bus/train from Downtown Toronto, the Eastern ends of Toronto (Scarborough), or areas of Durham (Pickering, Ajax) to the University can be anywhere between 1 and 2.5 hours one way, since you have to take multiple transit operators.
Additionally, when compared to Toronto,job opportunities in Oshawa and the Durham Region are scarce. It depends on the program you apply to. If you are applying to UOIT/Ontario Tech University, keep all these points in mind. It is not a bad university, but other factors need to be considered too.