Audibly, the HD218s are good, but not spectacular performers. While the impedance rating is a low 24Ωs, the Sennheiser phones need more power than either the V-Jays or their PX100 stable mates before they make a satisfying noise, and the bass response is more adequate than excellent. The sound is less bright and more balanced than the V-Jays and there's a bit more mid-range warmth to work with, but the output at the high-end sounds slightly muffled, and there's also some sibilance on cymbals.
It's a respectable sound for such a compact pair of headphones, but not in the same league as the V-Jays or iGrados. What's more, the usual curse of the closed-back headphone - a boxed-in, rather enclosed sound - applies, though you do get a wider soundstage and a brighter treble than with some budget closed-back phones I've tried.
The Sennheisers are at their best with low-key acoustic or jazz material, pop and lighter rock than they are with big beats, hip-hop or metal. The warm sound suits the funky Latin grooves of Quantic's Tradition in Transition album and the bright, eighties-styled pop sounds of The Juan MacLean's Accusations, but Public Enemy's By the Time I get to Arizona sounds subdued, it's rolling bass-line stripped of impact.
Daft Punk's Aerodynamic retains most of its infectious energy, though the beats don't have the punch they do with the V-Jays or iGrados, but DJ Shadow's The Private Press falls flat without the low-end raunchiness or top-end sparkle of rival cans. Mastodon's metal is a bit of a sibilant mess, but the Prefuse 73 ambient remix of Via Tania's Drift Away sounds sweet and enveloping. In other words, your mileage will vary according to your material.
On the upside, the HD218s are widely available for under £30, which makes them decent value for money, while they do a better job of sound isolation than either the iGrados or the PX100s. That said, the PX100s offer even better value for under £25, and the iGrados can be had at a similar price if you shop around. If you want the best sound at this price point, those should still be your best starting point.
Good isolation and decent bass response, but the sound overall isn't up there with Sennheiser's best at this price point.