I have visited it before, but not in a long time as I do not particularly like it. Some of its sources are good and scholarly (e.g., if I recall correctly they have Jeffrey’s 1938 study on the foreign vocabulary of the Qur’an posted somewhere on that site), but a lot of it is a particular type of apologetics I do not like: harping on translation as though exact equivalents can be drawn between Arabic and English (or Greek, or Latin, or Aramaic), referencing and pseudo-quoting anonymous Muslim theologians (in the form of “As a prominent Muslim theologian has said…” without naming him, and without sourcing the supposed quote, etc.), and presupposing of a common Christian worldview that underlies some of their points (e.g., stuff about Augustine and others which, as an Orthodox Christian, I find to detract from their mission).
I prefer to use historical sources to the extent that they are available. I’ve recommended it many times, and it is expensive, but if you can find it, Hoyland’s Seeing Islam as Others Saw It: A Survey and Evaluation of Christian, Jewish, and Zoroastrian Writings on Early Islam (Darwin Press, NJ 1997) is a wealth of such material. It is not intended for apologetic use (the “survey” part includes the author’s analyses of the origins of the texts, and he sees many of them as retreads of earlier anti-Jewish polemics), but it is also the only such compendium that I have seen, and as such is valuable for the material it includes (not only Greek and Latin, but also Syriac, Coptic, Ethiopic, Persian, Armenian, and even some Chinese texts). See also Griffith (who has written a lot on early Arab Christianity and its interaction with Islam), Grypeou et al (The Encounter of Eastern Christianity with Early Islam), etc. I had once also on this computer (dunno where it went) a translation of a wonderful Syriac treatise c.12th century from one of the fathers (Bar Hebraeus, perhaps?) that was dedicated to and named something like “On the Principles of Determining the Truth of Religion” which, while it did not reference Islam directly, nonetheless provided a brilliant defense of Christianity that probably very much had that in mind, given its time and place. Wish I could find that again… (including it in this post to see if it might jog the memories of any of our Syriac posters, honestly). There are several such early apologetics coming from the then still-largely-Syriac-speaking world. In addition, the aforementioned Griffith has described in his recent book on the Bible in Arabic the very first piece of Christian literature to ever appear in the Arabic language (i.e., the first original composition, predating even the dated Biblical manuscripts in the language) to be written anonymously circa mid-9th century and bearing the title On the Triune Nature of God…boy, would I love to get my hands on that somehow!
In short, Answering Islam is by no means the worst Christian apologetics site I’ve ever seen aimed at Muslims, but there are far superior sources out there that are largely without its shortcomings. No source is perfect (not even the scholarly ones I mentioned above), but some certainly are better than others, and I would put Answering Islam (and its Islamic counterpart, Answering Christianity) rather low on the totem pole.