First of all, there's nothing unreal about CNG, in fact the Orange Line buses in LA are CNG articulated buses. NYC has a fleet of hybrid buses, and I've even seen a fuel cell bus in service, though I think it was a unique example. The problems with Orange Line style BRT amount to the inability to provide crossing gates, the slowness of the buses, and the generally cramped interior of buses and lack of MU ability. Basically, what this amounts to is that service is considerably slower than a light rail line would have been (by at least 50%), and buses get more crowded. Another important issue is the narrowness of the busway, which has two lanes and no shoulder, with oncoming buses passing at 55 mph. It would have been safer with rails.

A side issue is that this is primarily a feeder service for the heavy rail Red Line, but the bus service has to run at half the headway, leading to bunching and a service of two buses every 10 minutes instead of one every five. Oh, and some sections of the pavement had to be replaced after something like 8 months, though I think they replaced asphalt with concrete in curves, so I think it should last a while longer this time around.