A messianic Jew is someone who believes that Yeshu came to be messiah to the Jewish people, and thus in order to follow him properly one needs to be Jewish. Thus they believe in all of the commandments of the Original Testament and practice them to varying degrees with varying interpretations based on the community they belong to. I have met a few Messianic Jews here in Israel who for all intents and purposes are Jewish and practice a halachically Jewish lifestyle - only they believe that Yeshu was Messiah and all that other nonsense. I also have a good friend in the states who was a chrstian and then declared himself a Messianic Jew and joined a community without going through the proper conversion cycle and his community is more like Messianic Reform Jews.