I think the bar is set so low for horror in Malayalam cinema that anything mildly intriguing can cause a few ripples among our largely unexposed audiences. The case in point is Phoenix, which can easily be bifurcated into a horror drama in the first half and a romantic tragedy in the second.
Between the two, the more engaging elements are in the first, and while the second promises an old-school romance, the dramatic dialogues often took me out of the setup. (This was the case in Aashiq Abu's reimagining of Neelavelicham too.) Of course, I understand the director's intention to portray the slowness of the '70s, and this works in parts. The integration of the cholera epidemic into the plot also offers a different backdrop, as opposed to the usual "killing off" of a central character to evoke grief.
From a writing standpoint, I think Midhun Manuel picked bits and pieces from various works (like the Insidious films and Gabriel Garcia Marquez's classic novel Love in the Time of Cholera), probably his personal favorites, and gave it his own spin. Sam CS' music works in parts, but there were too many songs in the second half, further hampering the flow. As a debut director, I feel Vishnu Bharathan is promising, and given a more fast-paced screenplay, he can truly shine. Some shot choices are solid, especially one that uses the split diopter lens. The visual effects are not bad.
Coming to the performances, Baby Aavni's "possessed" act was quite good. Aju Varghese adds one more feather to his cap in a role that initially requires him to be a chauvinist, and later an inquisitive (and somewhat scared) man of the house. Abhirami Bose looks good and even exudes the '70s girl aura, but the lipsync was off in places. Chandunadh's performance occasionally borders on the theatrical, but there's been visible progress over the years. Anoop Menon and the rest are adequate.
P. S. Where's that creepy scene of the priest (Rony David Raj) at the seaside cemetery that was in the trailer? In fact, that scene was what made me want to watch the film in the first place.