Sennheiser HD 650 vs Bose QuietComfort 25

The sound signature is near neutral but with a little emphasis on the lower frequencies. The bass is slightly forward with good punch and tightness. Explosions will have good rumble, without overpowering the other frequencies.
The mids are warm and clear, adding extra body to the sound. Game dialogue will be easy to hear.
Highs have good clarity, but are not forward in any way, so harshness is minimized.

The H650 is popular for its near neutral sound, which makes it quite versatile. The headphones can give a great casual listening, gaming, and movie watching experience yet are accurate enough for pro audio mixing. They are also lightweight and comfortable so you won't have any issues wearing them for hours.

Clamping force is not too tight. The ear pads and headband feature memory foam which are covered by velour material. The pads feel really soft on the head and allow airflow for minimized heat build-up/sweat.
The headband also features similar cushioning materials and minimizes pressure spots on the head.

The open ear cup design allows the sound to blend with your surroundings, giving it a natural width. It will also be easier to identify the direction of sounds, which can really help immersion.

The HD-650s do not feel heavy at all. They are usable for long music listening, movie or gaming sessions without feeling pain or strain on their head and neck.

While the cable connectors are proprietary, they can easily be removed from the ear cups with a firm pull. The popularity of these headphones means that there are a lot of aftermarket cables that can be bought.

The traveling case is small and provides room for spare batteries and other components. This makes it pretty portable, for those that can't or don't want to leave their headphones at work.

These headphones use a triple-A battery to power noise canceling. Should it run out of charge, it can easily be replaced.

With the feature switched on, you can really zone in on the music. Noise canceling is very effective at blocking out ambient noise, especially the lower frequencies. On a flight for example, engine noise is drastically reduced, as well as most of the sound from the conversations in your vicinity.

The QC25 feels comfortable even after wearing it for several hours. The pads go over the ear and feel soft, as the ample cushioning is covered with supple and high quality synthetic leather. Aside from the usual headband padding, it also has an inner Alcantara lining that feels really nice on the skin.

You have a number of options as to how you want to use these headphones' active noise canceling feature. You can either have the feature on or off while you are listening to music, or have noise canceling on without audio. This is a nifty feature if you just want to enjoy some peace and quiet when in a noisy place.

These headphones will not tire your head or neck out, even if you wear them for quite some time. These are pretty light at around 196 grams.

Sub-bass is a bit laid back, but the overall low-end production is punchy and with good extension. Mids are clear and forward so vocals, guitars and keys sound good with these. The upper treble is boosted, which results in good detail, but can also give harshness to the sound.
Overall, this is a really fun set of cans to listen to, especially if you just want to have a fun music listening experience.