It was good. I enjoyed myself but I do think it best to keep superpowers out of Arrow. It just creates logical nightmares.
The biggest glaring thing for me was Captain Boomerang is attacking Argus and he throws the two boomerangs at Oliver. Flash shows up and grabs the two boomerangs in the nick of time. Then Captain Boomerang throws some flash powder and "disappears" aka runs away. Meanwhile, Flash just stands there smiling at Oliver. Really? Not going to use your superspeed to chase down the bad guy or knock him unconscious? It's like at the end when they confront Captain Boomerang at the train station. The Flash grabs everyone off the platform for safety before he and Oliver confront the Captain. Why not just use the super speed to knock him out as he would clearly not be able to counterattack as shown by his reaction of just watching everyone disappear around him while Flash vacates them all. But no, they stand around talking to him allowing him to then activate the bombs.
I was also disappointed that a portion of the Arrow cast was relegated to the sidelines. Quinten, Laurel and Thea basically make cameos. No Ray Palmer. Nothing going on with Malcolm. Maybe he was hiding in some bushes watching Thea and I just didn't see him on a first watch.
Yes, The Flash did it better as it advanced The Flash storyline and even helped set things up with Arrow's storylines. Plus, The Flash involved all of its cast quite well. Even Singh finally started getting some screen time. I like to think the reason he approved the Flash taskforce is because the Flash stole his lunch. Way to be a hero, Barry. This episode had very little effect on The Flash show and even with Arrow's current season, it did very little with any of the moving pieces occurring right now. Worst of all, Felicity asks for help with looking into Sara's death by examining some DNA on The Flash but I guess she didn't bring the sample or files with her? So then Team S.T.A.R. labs shows up to help with the DNA except they are just there to pick it up and see how the Arrow lives? Finally, when they go, they say they will just call with the results. Thanks for dragging that thing to death.
For me, the best episodes of Arrow this season have been the first two episodes and Nyssa's return with that one being the best episode so far.