I like the list - it epitomises the Space Marines ethos, without being uncompetitive. However, I disagree with the use of Ironclads for one main reason - Low Troops Count. LTC is a crippling affliction that affects many SM armies in particular, which is why I post more about it in this forum than anywhere else, although perhaps a Tactica article is necessary as a reference tool...anyway, you have 3 Troops choices, in a 1500 list. Normally, this is sufficient, my suggested ratio being 1 for every 500pts or part thereof. On this occasion however, your Troops will bear the brunt of the fighting, and will
take casualties. Being able to Combat Squad the Bikes is excellent, and does put you up to 5 Scoring Units, however these units are susceptible to weight of fire, despite their high T, and, against Tau, IG, and Eldar in particular, will be slaughtered in a protracted firefight. To this end, I recommend replacing the Dreads with 3 Predator Destructors, to take out units such as Lootas and take the fire of Fire Prisms that would otherwise maul the Bikers, until they get into Melta range (2 Turns max, in normal circumstances)
By saving these points you will be able to take two more, smaller, Bike Squads, probably with Flamers to replace the HFs on the Ironclads, putting you up to 5 Troops. Any spare points can happily be invested in HF Land Speeders to support the Bike assualt, or HF/MM if possible. You have to remember that the main advantage you have as Vanilla Marines over Ravenwing when Bike'd up is numbers, take advantage!