I'm still using Opera 11.xx. Just at work I have Opera 12.xx. That browser line was effectively killed and there is nothing even remotely comparable. I tried to switch to both Chrome and FF several times, but it didn't went well. Now I use multiple browsers. One for normal web and one for stuff like gmail (that has trouble running in the old Opera).
Gmail's HTML-only mode works fine in Opera 12, and unless you really like the (imho slow and bloated) interface of regular gmail, it is better. The only issues I had were bulk deleting spam and trash, it took me only a 5 line userscript to add a "select-all" button and the problem is solved. Also worth mentioning that this interface isn't exactly html-only, it still has some assisting javascript like automatically completing typed addresses from your contacts.
