Visual Arts: Aidan Dunne reviews The Overlap Areas by Fergus Feehily at the Green on Red Gallery until Apr 16 (01-6713414), Ene-Liis Semper/Mark Raidpere at the Temple Bar Gallery until Apr 16 (01-6710073) and Echoes by David King at the Hallward Gallery until Apr 1 (01-6621482).

It's no disparagement to say that there is an elusive quality to Fergus Feehily's work in The Overlap Areas at Green on Red.

The title makes sense when you see the interlocking loops that feature recurrently in his paintings and notice that the accompanying book, a beautiful publication, is called A Venn Notebook. Venn diagrams are an indispensable means of visualisation in set theory, and the overlap areas are the spaces where sets intersect. We should probably think of Venn diagrams as a metaphor for what Feehily is in pursuit of in his painting: a fuzzy, in-between area where categories blur and merge.

On the evidence of his work past and present, he is interested in systems as well as sets, self-regulating systems in the sense of delicately balanced, tenuous, flexible structures, the subtle fabric of things, rather than rigid impositions.

Unexpected connections, disorientation, things not being what they seem, all come across as being particularly pleasing to him, but so too do random fluctuations, things that have minds of their own, chance accumulations. It makes sense that David Toop, who wrote the essay in A Venn Notebook, is a composer. Music inevitably comes to mind in relation to Feehily's feeling for structure: why it should be there, why it shouldn't be obvious.

There is a tact and modesty to what he does that is very appealing, as though he doesn't want to get in the way of the painting. When he sets out on a particular path in an individual piece, he very quickly tries to second-guess himself, so that he doesn't end up at a predictable destination. Sometimes the way to avoid that is to simply stop, or there is always the option of striking off in a different direction, or of covering his tracks. All these strategies are evident in different pieces.

A paradox here is that something that might look relatively subtle coming from someone else can appear heavy-handed in the context of his own work as a whole. I remember feeling that about one piece last year, in which the statement of pattern was unusually definite, followed through to the point of insistence. More usually even explicit systems, such as the alphabet, or repeat geometric patterns, are barely there.

If all this comes across as vague, as not helpfully descriptive, it should be considered in the context of the works themselves, and the elusive borderland they inhabit.

Estonian Ene-Liis Semper's Licked Room at the Temple Bar Gallery is just that, a room within a room, a clean white cube that the artist spent some time licking. This odd, ritualistic action was recorded on video and can be seen on three monitors in the space. We catch glimpses of onlookers in the background, clustered in the entrance. The artist, dressed in white, with close-cropped hair, sets about her self-imposed task with calm determination, and as though it was the most natural thing in the world.

Watching the video is likely to be in some measure an uncomfortable experience, partly because it's clear that the prolonged contact with walls and floor must be unpleasantly abrasive for her, and partly because the performance is like a form of mild self-abasement, it's an oddly intimate gesture. It recalls comparable works by Janine Antoni relating to obsessive compulsive behaviour, food and cleaning. One could add exploitation, in the context of Semper's piece.

The other video included in her show FF/REW uses the medium's temporal fluidity to look at the way irreversible actions can be based on transitory feelings. To the tender strains of the slow movement of a Beethoven piano concerto, a woman calmly hangs herself, but on video, the action is not necessarily final.

Semper has brought two pieces by another Estonian artist, Mark Raidpere, who will represent Estonia at the Venice Biennale later this year. Both Raidpere's videos are emotionally charged studies of his relationship with his parents.

In one he chronicles his father's apartment in a series of restless, lurching, impulsive camera movements suggestive of a troubled temperament, something confirmed by a staged but difficult, tearful conversation with his mother, the subject of the other video.

Actually, the conversation never gets off the ground and the piece is about what remains unspoken but is intensely felt. Does Raidpere cry on cue? It's hard to know, he seems upset, as though he were a method actor looking to some grief deep within himself to encourage the tears. So in a sense there is a mixture of real and fake, but an acknowledged mixture.

There's more than a touch of the Gothic to David King's exhibition Echoes at the Hallward Gallery. Views of gloomy woodland wreathed in heavy mist, graveyards, woodland huts, a castle on a lake under low, brooding cloud, a couple of panoramic views of enormous expanses of desolate mountainous moorland: all set a certain lowering mood, and they influence the way we look at the more ordinary, workaday scenes with which they are juxtaposed. These include a bus shelter and a terraced house by night.

The latter are painted in a fairly straight manner, though they too are dark images with an ominous edge. Many of King's paintings, particularly the larger ones, have frenetically detailed surfaces and tones weighted toward black.

The sheer elaboration of detail and the way they are worked give them a curdled, overdone quality - and not by accident. Peter Doig has done exactly that in his paintings, and he comes to mind in relation to several of King's pieces, though the latter doesn't push things half as far as Doig, who breaks through into a whole new area.

The work of Paul Winstanley, whose show has just opened at the Kerlin, is another point of comparison. The interplay of nostalgic or anachronistic elements with the wholly contemporary in King's painting engenders a feeling of the persistence of the Gothic imagination. But he also addresses the status of nature more generally, in terms of fantasies of alternative life, as in images of the hut in the woods, or the imposition of conifer woodland, or the wilderness as a backdrop for urban walkers.

It is a good but uneven show, uneven largely because there is more work than there needs to be in it. King certainly has an eye for striking images, including the aftermath of tree felling in the Slieve Blooms and a snowfall at the Sally Gap.