So far the new Wulfen have received mixed reviews. Some say that the game is turning back towards the assault phase while others say they aren't worth their points and this basically an exercise in pulling in the reins on Space Wolves - note the Iron Priest is now selected from the HQ slot and gains an additional wound. Just look to the Wolves Unleashed detachment in the Space Wolf codex - you can field up to six HQ and elites are optional... Nothing has really changed in that regard. Let's remained focused on the role of the Wulfen and how they can play out.
I am a student of the assault phase and that's how I play my armies. I played the 13th Company which was the first appearance of the Wulfen. It was a great army and could beat Chaos back when Chaos Space Marines were a true contender. This was during a phase of the game when transports were not popular and Wulfen had a rule called Animal Rage which basically gave a d6 extra movement that could be used with charging so it was very powerful at the time. The original Wulfen had no options for melee wargear but were WS5, had a high number of attacks and were I5. Basically they could lay down enough wounds it would force enough failed saves versus any unit. You had to attach a Wolf Priest who could control their movement and arm him a thunderhammer so he could take out the big stuff like high armor.
The new Wulfen are only WS4 but are just as fast, have just as many attacks if not more and have access to some really awesome melee weapons such as Frost Claws. The new Wulfen can run and charge which means once they are in range they will devastate enemy lines. The key to their success will rely upon their delivery system. They are bulky too but who is going to attempt to assault out of a drop pod unless it has special rules ? Basically you can fit up to five in a Stormclaw which I think is a good starting point for using this unit. The Stormclaw has a transport capacity of 16 models so up to eight Wulfen can embsrk which is a solid number. Probably one unit of Wulfen is enough... Armed with the right wargear they can take down Stormsurges and Wraithknights on the charge. The new Wulen have two wounds apiece as well so they can weather even Tau Overwatch.
To me the game is changing at a rapid pace right before our very eyes and I think the new Wulfen will be a game winner. Harlequins didn't pan out well because they are so fragile and die to bolters. Wulfen on the other hand are hard as nails.