well, the problem is that once they get into power they're completely moribund and start collapsing into factions. At least the LDP are united in the sheer determination to protect established interests. (I think the LDP are closest you will come to an undiluted small-"c" conservative party)
Their main problem was that they decided to copy the LDP way of doing things. The allocation of ministers in 2009 was based on seniority (just like LDP) and internal organization was based on factions (just like LDP). Problem with that is LDP is powerful based on the local Clientelism and DPJ can never match LDP in that respect so replicating their style of organization would lead to disaster which it did.