Getting onto usability, we're not disappointed by the Aspire 5551's matt-black, isolation keyboard. It has an excellent layout with a proper UK-style Enter key and a full number pad with a full-size Insert/0 key. Despite their shallow appearance, the keys offer a good amount of travel with reasonably positive feedback - though it's not quite as well-defined as on some earlier Aspire models we looked at. There's also some flex towards the centre, but it's not enough to spoil a generally pleasant typing experience.
With its large, smooth surface the multi-gesture touchpad is likewise a pleasure to use, and its positioning means it never interferes with typing. Both of the pad's buttons are incorporated into a single rocker switch, which is just a tad too stiff for our liking but still usable.
As far as the 15.6in LED-backlit screen goes, aside from its aforementioned glossy finish it sports a 1,366 x 768 resolution. In a reversal of the usual bias, our greyscale tests revealed that it favoured light detail over dark, giving you pure whites at the cost of dark detail in games and films. Viewing angles are also pretty mediocre, with vertical ones slightly above average but horizontal ones letting the side down, leaving you with quite a narrow field of view.
On the positives side there is minimal banding, backlighting is even without distracting light-bleed, and excellent sharpness results in good legibility of small fonts. As with most laptop displays, that of the Aspire 5551 is absolutely fine for daily productivity, but it's not the best for entertainment and certainly not suited to graphical work.
Acer's 3D Sonic speakers are more impressive. Aside from some distortion at their maximum volume and a slight lack of bass that's common to most laptop efforts, they produce a decent soundstage with a bit of punch and clarity. A good set of headphones will give far better performance, but here that's a recommendation rather than a necessity.